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[R-devel] Source Code for function

17 messages · Bert Gunter, Golden, Shelby, Jiefei Wang +4 more

Original
Golden, Shelby
# 
Hi all,

I have been attempting to access the source code for the keyword ?function? to better understand how it assigns and stores logical inputs, like in the subset() [base] function. Does anyone know how I can access the source code for this?

For example, if I have
norm <- function(x){
      sqrt(x%*%x))
}
I am looking for the source code for the ?function? portion, highlighted in red.

Thank you for your time and assistance,
Shelby Golden
Lab Researcher Technician
Dr. Russell Bowler?s Lab
Department of Medicine
National Jewish Health in Denver, CO
Phone: (303) 270-2598

NOTICE: This email message is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message.
Bert Gunter
# 
1. This is a plain text list; all html is stripped. So there is no red
highlighting.

2. There is no "source code" for "function" -- it is a reserved keyword.
Or are you looking for R's formal grammar -- e.g. how it parses input to
determine correct syntax?



Bert Gunter

"The trouble with having an open mind is that people keep coming along and
sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
On Fri, Sep 6, 2019 at 8:51 AM Golden, Shelby <GoldenS at njhealth.org> wrote:

            

      
      
      
    

        

      
      
    

        

  
  


  


      

    

    

      
      

        


  

        

      Golden, Shelby
    

    

      
      #
    

  


  

      
Hello Bert,

Thank you for the reply and your clarifications. Yes, it might be helpful to look into R?s formal grammar to see how ?function? parses input to delegate correct syntax. Is that accessible online?

Thank you,
Shelby


From: Bert Gunter <bgunter.4567 at gmail.com>
Date: Friday, September 6, 2019 at 10:44 AM
To: "Golden, Shelby" <GoldenS at NJHealth.org>
Cc: "r-help at R-project.org" <r-help at r-project.org>, "Gillenwater, Lucas" <GILLENWATERL at NJHEALTH.ORG>
Subject: Re: [R] [R-devel] Source Code for function

1. This is a plain text list; all html is stripped. So there is no red highlighting.

2. There is no "source code" for "function" -- it is a reserved keyword.
Or are you looking for R's formal grammar -- e.g. how it parses input to determine correct syntax?



Bert Gunter

"The trouble with having an open mind is that people keep coming along and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )

        
On Fri, Sep 6, 2019 at 8:51 AM Golden, Shelby <GoldenS at njhealth.org<mailto:GoldenS at njhealth.org>> wrote:

        
Hi all,

I have been attempting to access the source code for the keyword ?function? to better understand how it assigns and stores logical inputs, like in the subset() [base] function. Does anyone know how I can access the source code for this?

For example, if I have
norm <- function(x){
      sqrt(x%*%x))
}
I am looking for the source code for the ?function? portion, highlighted in red.

Thank you for your time and assistance,
Shelby Golden
Lab Researcher Technician
Dr. Russell Bowler?s Lab
Department of Medicine
National Jewish Health in Denver, CO
Phone: (303) 270-2598

NOTICE: This email message is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message.

______________________________________________
R-help at r-project.org<mailto:R-help at r-project.org> mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help<http://mx2.njhealth.org:32224/?dmVyPTEuMDAxJiZmMWRiYmMxZjFmNmI5ZDBkMz01RDcyOEQwN18yMjk2OF8zOTk2XzEmJjljNzlmMDA4YWRmZTZjMz0xMjMzJiZ1cmw9aHR0cHMlM0ElMkYlMkZzdGF0JTJFZXRoeiUyRWNoJTJGbWFpbG1hbiUyRmxpc3RpbmZvJTJGci1oZWxw>
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html<http://mx2.njhealth.org:32224/?dmVyPTEuMDAxJiZlMTkwYmMwMzFlNjk4ZTAzNz01RDcyOEQwN18yMjk2OF8zOTk2XzEmJmFkYTkxMWRkMWRhZTFkNz0xMjMzJiZ1cmw9aHR0cCUzQSUyRiUyRnd3dyUyRVItcHJvamVjdCUyRW9yZyUyRnBvc3RpbmctZ3VpZGUlMkVodG1s>
and provide commented, minimal, self-contained, reproducible code.

  
  


  


      

    

    

      
      

        


  

        

      Jiefei Wang
    

    

      
      #
    

  


  

      
Hi Shelby,

Not quite sure what you are trying to do. Mine might be off-topic but have
you seen this document?

http://adv-r.had.co.nz/Functions.html#function-components

It illustrates the components of a function.

Best,
Jiefei

        
On Fri, Sep 6, 2019 at 11:52 AM Golden, Shelby <GoldenS at njhealth.org> wrote:

        

            

      
      
      
    

        

      
      
    

        

  
  


  


      

    

    

      
      

        


  

        

      Jiefei Wang
    

    

      
      #
    

  


  

      
If you are looking for an R code parser, I think the `parse` and `eval`
function might be a good start point. See the example below.

            

      
      
      
    

        
expression(function(x)message(x))

            

      
      
      
    

        
function(x)message(x)

Best,
Jiefei

        
On Fri, Sep 6, 2019 at 12:55 PM Golden, Shelby <GoldenS at njhealth.org> wrote:

        

            

      
      
      
    

        

      
      
    

        

  
  


  


      

    

    

      
      

        


  

        

      Bert Gunter
    

    

      
      #
    

  


  

      
The following may be of use (it gives the parse tree of the text):

            

      
      
      
    

        
function(x) x %*% x

            

      
      
      
    

        
`function`

            

      
      
      
    

        
$x

            

      
      
      
    

        
x %*% x

            

      
      
      
    

        
`%*%`

            

      
      
      
    

        
x

            

      
      
      
    

        
x


Bert Gunter

        
On Fri, Sep 6, 2019 at 10:14 AM Wang Jiefei <szwjf08 at gmail.com> wrote:

        

            

      
      
      
    

        

      
      
    

            

      
      
      
    

        

  
  


  


      

    

    

      
      

        


  

        

      Richard M. Heiberger
    

    

      
      #
    

  


  

      
You might also want to look at the codetools package, for example the
showTree function " Prints a Lisp-style representation of R
expression."

            

      
      
      
    

        
(%*% x x)

            

      
      
      
    

        
(+ a b)

            

      
      
      
    

        
(~ y (+ a b))

        
On Fri, Sep 6, 2019 at 2:30 PM Bert Gunter <bgunter.4567 at gmail.com> wrote:

            

      
      
      
    

        

      
      
    

            

      
      
      
    

        

      
      
    

  
  


  


      

    

    

      
      

        


  

        

      Golden, Shelby
    

    

      
      #
    

  


  

      
Thank you all for your reply. I should clarify, that I am looking to understand why the keyword function can take a logical argument (eg: x<4) and use that later inside the function's definition for logical evaluations.

Consider this example, which is a simplification of getAnywhere(subset.data.frame):
x = data.frame("Col1" = c(1, 2, 3, 4, 5), "Col2" = c(6, 7, 8, 9, 10))
test <- function(x, logic){
	e <- substitute(logic)
	r <- eval(e, x, parent.frame())
	r[r]
}


Shelby
 

?On 9/6/19, 1:02 PM, "R-help on behalf of Richard M. Heiberger" <r-help-bounces at r-project.org on behalf of rmh at temple.edu> wrote:

    You might also want to look at the codetools package, for example the
    showTree function " Prints a Lisp-style representation of R
    expression."
    
    > library(codetools)
    
    > showTree(quote(x %*% x))
    (%*% x x)
    > showTree(quote(a+b))
    (+ a b)
    > showTree(quote(y ~ a+b))
    (~ y (+ a b))

        
On Fri, Sep 6, 2019 at 2:30 PM Bert Gunter <bgunter.4567 at gmail.com> wrote:

        
>
    > The following may be of use (it gives the parse tree of the text):
    >
    > > z <- as.list(parse(text = "function(x)x %*% x"))
    > > z[[1]]
    > function(x) x %*% x
    > > z[[c(1,1)]]
    > `function`
    > > z[[c(1,2)]]
    > $x
    > > z[[c(1,3)]]
    > x %*% x
    > > z[[c(1,3,1)]]
    > `%*%`
    > > z[[c(1,3,2)]]
    > x
    > > z[[c(1,3,3)]]
    > x
    >
    >
    > Bert Gunter
    >
    >
    >

        
> On Fri, Sep 6, 2019 at 10:14 AM Wang Jiefei <szwjf08 at gmail.com> wrote:

        
>
    > > If you are looking for an R code parser, I think the `parse` and `eval`
    > > function might be a good start point. See the example below.
    > >
    > > > parse(text="function(x)message(x)")
    > > expression(function(x)message(x))
    > > > eval(parse(text="function(x)message(x)"))
    > > function(x)message(x)
    > >
    > > Best,
    > > Jiefei
    > >
    > > On Fri, Sep 6, 2019 at 12:55 PM Golden, Shelby <GoldenS at njhealth.org>

        
> > wrote:

        
> >
    > >> Hello Bert,
    > >>
    > >> Thank you for the reply and your clarifications. Yes, it might be helpful
    > >> to look into R?s formal grammar to see how ?function? parses input to
    > >> delegate correct syntax. Is that accessible online?
    > >>
    > >> Thank you,
    > >> Shelby
    > >>
    > >>
    > >> From: Bert Gunter <bgunter.4567 at gmail.com>
    > >> Date: Friday, September 6, 2019 at 10:44 AM
    > >> To: "Golden, Shelby" <GoldenS at NJHealth.org>
    > >> Cc: "r-help at R-project.org" <r-help at r-project.org>, "Gillenwater, Lucas" <
    > >> GILLENWATERL at NJHEALTH.ORG>
    > >> Subject: Re: [R] [R-devel] Source Code for function
    > >>
    > >> 1. This is a plain text list; all html is stripped. So there is no red
    > >> highlighting.
    > >>
    > >> 2. There is no "source code" for "function" -- it is a reserved keyword.
    > >> Or are you looking for R's formal grammar -- e.g. how it parses input to
    > >> determine correct syntax?
    > >>
    > >>
    > >>
    > >> Bert Gunter
    > >>
    > >> "The trouble with having an open mind is that people keep coming along
    > >> and sticking things into it."
    > >> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
    > >>
    > >>
    > >> On Fri, Sep 6, 2019 at 8:51 AM Golden, Shelby <GoldenS at njhealth.org

        
> >> <mailto:GoldenS at njhealth.org>> wrote:

        
> >> Hi all,
    > >>
    > >> I have been attempting to access the source code for the keyword
    > >> ?function? to better understand how it assigns and stores logical inputs,
    > >> like in the subset() [base] function. Does anyone know how I can access the
    > >> source code for this?
    > >>
    > >> For example, if I have
    > >> norm <- function(x){
    > >>       sqrt(x%*%x))
    > >> }
    > >> I am looking for the source code for the ?function? portion, highlighted
    > >> in red.
    > >>
    > >> Thank you for your time and assistance,
    > >> Shelby Golden
    > >> Lab Researcher Technician
    > >> Dr. Russell Bowler?s Lab
    > >> Department of Medicine
    > >> National Jewish Health in Denver, CO
    > >> Phone: (303) 270-2598
    > >>
    > >> NOTICE: This email message is for the sole use of the intended
    > >> recipient(s) and may contain confidential and privileged information. Any
    > >> unauthorized review, use, disclosure or distribution is prohibited. If you
    > >> are not the intended recipient, please contact the sender by reply email
    > >> and destroy all copies of the original message.
    > >>         [[alternative HTML version deleted]]
    > >>
    > >> ______________________________________________
    > >> R-help at r-project.org<mailto:R-help at r-project.org> mailing list -- To
    > >> UNSUBSCRIBE and more, see
    > >> https://stat.ethz.ch/mailman/listinfo/r-help<
    > >> http://mx2.njhealth.org:32224/?dmVyPTEuMDAxJiZmMWRiYmMxZjFmNmI5ZDBkMz01RDcyOEQwN18yMjk2OF8zOTk2XzEmJjljNzlmMDA4YWRmZTZjMz0xMjMzJiZ1cmw9aHR0cHMlM0ElMkYlMkZzdGF0JTJFZXRoeiUyRWNoJTJGbWFpbG1hbiUyRmxpc3RpbmZvJTJGci1oZWxw
    > >> >
    > >> PLEASE do read the posting guide
    > >> http://www.R-project.org/posting-guide.html<
    > >> http://mx2.njhealth.org:32224/?dmVyPTEuMDAxJiZlMTkwYmMwMzFlNjk4ZTAzNz01RDcyOEQwN18yMjk2OF8zOTk2XzEmJmFkYTkxMWRkMWRhZTFkNz0xMjMzJiZ1cmw9aHR0cCUzQSUyRiUyRnd3dyUyRVItcHJvamVjdCUyRW9yZyUyRnBvc3RpbmctZ3VpZGUlMkVodG1s
    > >> >
    > >> and provide commented, minimal, self-contained, reproducible code.
    > >>
    > >>         [[alternative HTML version deleted]]
    > >>
    > >> ______________________________________________
    > >> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
    > >> https://stat.ethz.ch/mailman/listinfo/r-help
    > >> PLEASE do read the posting guide
    > >> http://www.R-project.org/posting-guide.html
    > >> and provide commented, minimal, self-contained, reproducible code.
    > >>
    > >
    >
    >         [[alternative HTML version deleted]]
    >
    > ______________________________________________
    > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
    > https://stat.ethz.ch/mailman/listinfo/r-help
    > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
    > and provide commented, minimal, self-contained, reproducible code.
    
    ______________________________________________
    R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
    https://stat.ethz.ch/mailman/listinfo/r-help
    PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
    and provide commented, minimal, self-contained, reproducible code.
    


NOTICE: This email message is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message.

  
  


  


      

    

    

      
      

        


  

        

      Golden, Shelby
    

    

      
      #
    

  


  

      
Hello Jiefei,

Missed this in the subsequent emails. That is a very intriguing article, but I do not believe that it quite answers my question. Regardless, I will review it, so thank you for sending it my way!

Respectfully,
Shelby


From: Wang Jiefei <szwjf08 at gmail.com>
Date: Friday, September 6, 2019 at 11:10 AM
To: "Golden, Shelby" <GoldenS at NJHealth.org>
Cc: "r-help at R-project.org" <r-help at r-project.org>, "Gillenwater, Lucas" <GILLENWATERL at NJHEALTH.ORG>
Subject: Re: [R] [R-devel] Source Code for function

Hi Shelby,

Not quite sure what you are trying to do. Mine might be off-topic but have you seen this document?

http://adv-r.had.co.nz/Functions.html#function-components<http://mx1.njhealth.org:32224/?dmVyPTEuMDAxJiYzZDQ2Y2Y3YzhmYmIwZmMzMz01RDcyOTJGNl81MzQ2N180NjY0XzEmJjBjMTRiYjE5NTI5MjI2MD0xMjMzJiZ1cmw9aHR0cCUzQSUyRiUyRmFkdi1yJTJFaGFkJTJFY28lMkVueiUyRkZ1bmN0aW9ucyUyRWh0bWwlMjNmdW5jdGlvbi1jb21wb25lbnRz>

It illustrates the components of a function.

Best,
Jiefei

        
On Fri, Sep 6, 2019 at 11:52 AM Golden, Shelby <GoldenS at njhealth.org<mailto:GoldenS at njhealth.org>> wrote:

        
Hi all,

I have been attempting to access the source code for the keyword ?function? to better understand how it assigns and stores logical inputs, like in the subset() [base] function. Does anyone know how I can access the source code for this?

For example, if I have
norm <- function(x){
      sqrt(x%*%x))
}
I am looking for the source code for the ?function? portion, highlighted in red.

Thank you for your time and assistance,
Shelby Golden
Lab Researcher Technician
Dr. Russell Bowler?s Lab
Department of Medicine
National Jewish Health in Denver, CO
Phone: (303) 270-2598

NOTICE: This email message is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message.

______________________________________________
R-help at r-project.org<mailto:R-help at r-project.org> mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help<http://mx1.njhealth.org:32224/?dmVyPTEuMDAxJiYyODRhOWIzMTgzZmQ0ZWQ0Nz01RDcyOTJGNl81MzQ2N180NjY0XzEmJmVlZTUyYjI5NzMzNjQ2Mz0xMjMzJiZ1cmw9aHR0cHMlM0ElMkYlMkZzdGF0JTJFZXRoeiUyRWNoJTJGbWFpbG1hbiUyRmxpc3RpbmZvJTJGci1oZWxw>
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html<http://mx1.njhealth.org:32224/?dmVyPTEuMDAxJiYyZTRkOGI3YTgzZTE0ZmQ2Nj01RDcyOTJGNl81MzQ2N180NjY0XzEmJmRlMDExYWY5OTJlM2Y2Nj0xMjMzJiZ1cmw9aHR0cCUzQSUyRiUyRnd3dyUyRVItcHJvamVjdCUyRW9yZyUyRnBvc3RpbmctZ3VpZGUlMkVodG1s>
and provide commented, minimal, self-contained, reproducible code.

  
  


  


      

    

    

      
      

        


  

        

      David Winsemius
    

    

      
      #
    

  


  

      
On 9/6/19 1:07 PM, Golden, Shelby wrote:

            

      
      
      
    

        
x<4 is not really a logical argument in that context. It is rather an 
expression and will remain an expression until it needs to be evaluated. 
See this even simpler example:


 ?test <- function(x, logic, ... ){
 ???? e <- deparse( substitute(logic))
 ???? #r <- eval(e, x, parent.frame())
 ???? e
 ?}
 ?test(4, x<4)
#[1] "x < 4"


 ?test(4, is.logical(x < 4) )
[1] "is.logical(x < 4)"


Some of this you have already been told, but appears necessary to 
repeat. Expressions given to `function` are not necessarily evaluated. 
They will be evaluated if assigned names.


test(4, zed = is.logical(x < 4) )
#[1] ""

The function()-function will parse the contents of the parentheses for 
number of arguments and for parse()-ability. It will evaluate named 
arguments created with "=". In the context of parsing the formals of a 
function the "=" operator is different than the "<-" function.

The substitute function will not evaluate (since in the language of R 
operations it is "special"), but rather checks that the expression can 
be parsed by R's rules, i.e. is a valid parse tree. `deparse` returns 
the original character representation.

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Golden, Shelby
    

    

      
      #
    

  


  

      
Afternoon, David,

Thank you for your suggestions and insight. I have previously utilized parse, but in my exploration to improve my coding technique I came across this comment in stackoverflow.com (https://stackoverflow.com/questions/1743698/evaluate-expression-given-as-a-string - comment left Martin Maechler). In it, he suggests that usage parse is not a good method, saying that it is "rarely an efficient or safe means to construct expressions (or calls)". 

Perhaps you, or others in this community, disagree with what Martin has to say about parse in this application?

Shelby

        
?On 9/6/19, 3:10 PM, "David Winsemius" <dwinsemius at comcast.net> wrote:

        

        
On 9/6/19 1:07 PM, Golden, Shelby wrote:

        
> Thank you all for your reply. I should clarify, that I am looking to understand why the keyword function can take a logical argument (eg: x<4) and use that later inside the function's definition for logical evaluations.
    >
    > Consider this example, which is a simplification of getAnywhere(subset.data.frame):
    > x = data.frame("Col1" = c(1, 2, 3, 4, 5), "Col2" = c(6, 7, 8, 9, 10))
    > test <- function(x, logic){
    > 	e <- substitute(logic)
    > 	r <- eval(e, x, parent.frame())
    > 	r[r]
    > }
    
    x<4 is not really a logical argument in that context. It is rather an 
    expression and will remain an expression until it needs to be evaluated. 
    See this even simpler example:
    
    
      test <- function(x, logic, ... ){
          e <- deparse( substitute(logic))
          #r <- eval(e, x, parent.frame())
          e
      }
      test(4, x<4)
    #[1] "x < 4"
    
    
      test(4, is.logical(x < 4) )
    [1] "is.logical(x < 4)"
    
    
    Some of this you have already been told, but appears necessary to 
    repeat. Expressions given to `function` are not necessarily evaluated. 
    They will be evaluated if assigned names.
    
    
    test(4, zed = is.logical(x < 4) )
    #[1] ""
    
    The function()-function will parse the contents of the parentheses for 
    number of arguments and for parse()-ability. It will evaluate named 
    arguments created with "=". In the context of parsing the formals of a 
    function the "=" operator is different than the "<-" function.
    
    The substitute function will not evaluate (since in the language of R 
    operations it is "special"), but rather checks that the expression can 
    be parsed by R's rules, i.e. is a valid parse tree. `deparse` returns 
    the original character representation.
    
    -- 
    
    David
    
    
    >
    > Shelby
    >   
    >
    > On 9/6/19, 1:02 PM, "R-help on behalf of Richard M. Heiberger" <r-help-bounces at r-project.org on behalf of rmh at temple.edu> wrote:
    >
    >      You might also want to look at the codetools package, for example the
    >      showTree function " Prints a Lisp-style representation of R
    >      expression."
    >      
    >      > library(codetools)
    >      
    >      > showTree(quote(x %*% x))
    >      (%*% x x)
    >      > showTree(quote(a+b))
    >      (+ a b)
    >      > showTree(quote(y ~ a+b))
    >      (~ y (+ a b))
    >

        
>      On Fri, Sep 6, 2019 at 2:30 PM Bert Gunter <bgunter.4567 at gmail.com> wrote:

        
>      >
    >      > The following may be of use (it gives the parse tree of the text):
    >      >
    >      > > z <- as.list(parse(text = "function(x)x %*% x"))
    >      > > z[[1]]
    >      > function(x) x %*% x
    >      > > z[[c(1,1)]]
    >      > `function`
    >      > > z[[c(1,2)]]
    >      > $x
    >      > > z[[c(1,3)]]
    >      > x %*% x
    >      > > z[[c(1,3,1)]]
    >      > `%*%`
    >      > > z[[c(1,3,2)]]
    >      > x
    >      > > z[[c(1,3,3)]]
    >      > x
    >      >
    >      >
    >      > Bert Gunter
    >      >
    >      >
    >      >

        
>      > On Fri, Sep 6, 2019 at 10:14 AM Wang Jiefei <szwjf08 at gmail.com> wrote:

        
>      >
    >      > > If you are looking for an R code parser, I think the `parse` and `eval`
    >      > > function might be a good start point. See the example below.
    >      > >
    >      > > > parse(text="function(x)message(x)")
    >      > > expression(function(x)message(x))
    >      > > > eval(parse(text="function(x)message(x)"))
    >      > > function(x)message(x)
    >      > >
    >      > > Best,
    >      > > Jiefei
    >      > >
    >      > > On Fri, Sep 6, 2019 at 12:55 PM Golden, Shelby <GoldenS at njhealth.org>

        
>      > > wrote:

        
>      > >
    >      > >> Hello Bert,
    >      > >>
    >      > >> Thank you for the reply and your clarifications. Yes, it might be helpful
    >      > >> to look into R?s formal grammar to see how ?function? parses input to
    >      > >> delegate correct syntax. Is that accessible online?
    >      > >>
    >      > >> Thank you,
    >      > >> Shelby
    >      > >>
    >      > >>
    >      > >> From: Bert Gunter <bgunter.4567 at gmail.com>
    >      > >> Date: Friday, September 6, 2019 at 10:44 AM
    >      > >> To: "Golden, Shelby" <GoldenS at NJHealth.org>
    >      > >> Cc: "r-help at R-project.org" <r-help at r-project.org>, "Gillenwater, Lucas" <
    >      > >> GILLENWATERL at NJHEALTH.ORG>
    >      > >> Subject: Re: [R] [R-devel] Source Code for function
    >      > >>
    >      > >> 1. This is a plain text list; all html is stripped. So there is no red
    >      > >> highlighting.
    >      > >>
    >      > >> 2. There is no "source code" for "function" -- it is a reserved keyword.
    >      > >> Or are you looking for R's formal grammar -- e.g. how it parses input to
    >      > >> determine correct syntax?
    >      > >>
    >      > >>
    >      > >>
    >      > >> Bert Gunter
    >      > >>
    >      > >> "The trouble with having an open mind is that people keep coming along
    >      > >> and sticking things into it."
    >      > >> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
    >      > >>
    >      > >>
    >      > >> On Fri, Sep 6, 2019 at 8:51 AM Golden, Shelby <GoldenS at njhealth.org

        
>      > >> <mailto:GoldenS at njhealth.org>> wrote:

        
>      > >> Hi all,
    >      > >>
    >      > >> I have been attempting to access the source code for the keyword
    >      > >> ?function? to better understand how it assigns and stores logical inputs,
    >      > >> like in the subset() [base] function. Does anyone know how I can access the
    >      > >> source code for this?
    >      > >>
    >      > >> For example, if I have
    >      > >> norm <- function(x){
    >      > >>       sqrt(x%*%x))
    >      > >> }
    >      > >> I am looking for the source code for the ?function? portion, highlighted
    >      > >> in red.
    >      > >>
    >      > >> Thank you for your time and assistance,
    >      > >> Shelby Golden
    >      > >> Lab Researcher Technician
    >      > >> Dr. Russell Bowler?s Lab
    >      > >> Department of Medicine
    >      > >> National Jewish Health in Denver, CO
    >      > >> Phone: (303) 270-2598
    >      > >>
    >      > >> NOTICE: This email message is for the sole use of the intended
    >      > >> recipient(s) and may contain confidential and privileged information. Any
    >      > >> unauthorized review, use, disclosure or distribution is prohibited. If you
    >      > >> are not the intended recipient, please contact the sender by reply email
    >      > >> and destroy all copies of the original message.
    >      > >>         [[alternative HTML version deleted]]
    >      > >>
    >      > >> ______________________________________________
    >      > >> R-help at r-project.org<mailto:R-help at r-project.org> mailing list -- To
    >      > >> UNSUBSCRIBE and more, see
    >      > >> https://stat.ethz.ch/mailman/listinfo/r-help<
    >      > >> http://mx2.njhealth.org:32224/?dmVyPTEuMDAxJiZmMWRiYmMxZjFmNmI5ZDBkMz01RDcyOEQwN18yMjk2OF8zOTk2XzEmJjljNzlmMDA4YWRmZTZjMz0xMjMzJiZ1cmw9aHR0cHMlM0ElMkYlMkZzdGF0JTJFZXRoeiUyRWNoJTJGbWFpbG1hbiUyRmxpc3RpbmZvJTJGci1oZWxw
    >      > >> >
    >      > >> PLEASE do read the posting guide
    >      > >> http://www.R-project.org/posting-guide.html<
    >      > >> http://mx2.njhealth.org:32224/?dmVyPTEuMDAxJiZlMTkwYmMwMzFlNjk4ZTAzNz01RDcyOEQwN18yMjk2OF8zOTk2XzEmJmFkYTkxMWRkMWRhZTFkNz0xMjMzJiZ1cmw9aHR0cCUzQSUyRiUyRnd3dyUyRVItcHJvamVjdCUyRW9yZyUyRnBvc3RpbmctZ3VpZGUlMkVodG1s
    >      > >> >
    >      > >> and provide commented, minimal, self-contained, reproducible code.
    >      > >>
    >      > >>         [[alternative HTML version deleted]]
    >      > >>
    >      > >> ______________________________________________
    >      > >> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
    >      > >> https://stat.ethz.ch/mailman/listinfo/r-help
    >      > >> PLEASE do read the posting guide
    >      > >> http://www.R-project.org/posting-guide.html
    >      > >> and provide commented, minimal, self-contained, reproducible code.
    >      > >>
    >      > >
    >      >
    >      >         [[alternative HTML version deleted]]
    >      >
    >      > ______________________________________________
    >      > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
    >      > https://stat.ethz.ch/mailman/listinfo/r-help
    >      > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
    >      > and provide commented, minimal, self-contained, reproducible code.
    >      
    >      ______________________________________________
    >      R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
    >      https://stat.ethz.ch/mailman/listinfo/r-help
    >      PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
    >      and provide commented, minimal, self-contained, reproducible code.
    >      
    >
    >
    > NOTICE: This email message is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message.
    > ______________________________________________
    > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
    > https://stat.ethz.ch/mailman/listinfo/r-help
    > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
    > and provide commented, minimal, self-contained, reproducible code.

  
  


  


      

    

    

      
      

        


  

        

      Peter Dalgaard
    

    

      
      #
    

  


  

      
Um... Let's get the concepts straight:

The "function" function doesn't evaluate anything. It just takes the list of formal arguments (including default expressions), the function body, and the current evaluation environment, and stiches them together into a function object, known as a "closure".

The action happens when a function is _called_. Then the actual arguments are combined with the formals, and the body expression is evaluated. You will find the source code for this in src/main/eval.c. It is a pretty complex beast, but the essential point for the present discussion is that actual arguments in function calls are passed in the form of so-called promises. These contain the expression passed, so that substitute() can extract it. It also enables lazy evaluation: putting off argument evaluation until the value is actually needed (possibly never).  

-pd

            

      
      
      
    

        

      
      
    

            

      
      
      
    

        

      
      
    

        

      
      
    

            

      
      
      
    

        

      
      
    

        

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Golden, Shelby
    

    

      
      #
    

  


  

      
Afternoon, Peter,

Thank you for your concise but informative reply, and for a link to the source code. These complex concepts do answer my question spot on, so thank you for taking the time to put them all together and summarizing them for me.

Is the standard nomenclature for arguments in function calls "promises"? I would like to look into this concept further. If there are other concepts you think I should look into further too, I would be happy to include those as well.

Regards,
Shelby

        
?On 9/6/19, 4:02 PM, "peter dalgaard" <pdalgd at gmail.com> wrote:

        
Um... Let's get the concepts straight:
    
    The "function" function doesn't evaluate anything. It just takes the list of formal arguments (including default expressions), the function body, and the current evaluation environment, and stiches them together into a function object, known as a "closure".
    
    The action happens when a function is _called_. Then the actual arguments are combined with the formals, and the body expression is evaluated. You will find the source code for this in src/main/eval.c. It is a pretty complex beast, but the essential point for the present discussion is that actual arguments in function calls are passed in the form of so-called promises. These contain the expression passed, so that substitute() can extract it. It also enables lazy evaluation: putting off argument evaluation until the value is actually needed (possibly never).  
    
    -pd

        
> On 6 Sep 2019, at 23:10 , David Winsemius <dwinsemius at comcast.net> wrote:

        
> 
    >

        
> On 9/6/19 1:07 PM, Golden, Shelby wrote:

        
>> Thank you all for your reply. I should clarify, that I am looking to understand why the keyword function can take a logical argument (eg: x<4) and use that later inside the function's definition for logical evaluations.
    >> 
    >> Consider this example, which is a simplification of getAnywhere(subset.data.frame):
    >> x = data.frame("Col1" = c(1, 2, 3, 4, 5), "Col2" = c(6, 7, 8, 9, 10))
    >> test <- function(x, logic){
    >> 	e <- substitute(logic)
    >> 	r <- eval(e, x, parent.frame())
    >> 	r[r]
    >> }
    > 
    > x<4 is not really a logical argument in that context. It is rather an expression and will remain an expression until it needs to be evaluated. See this even simpler example:
    > 
    > 
    >  test <- function(x, logic, ... ){
    >      e <- deparse( substitute(logic))
    >      #r <- eval(e, x, parent.frame())
    >      e
    >  }
    >  test(4, x<4)
    > #[1] "x < 4"
    > 
    > 
    >  test(4, is.logical(x < 4) )
    > [1] "is.logical(x < 4)"
    > 
    > 
    > Some of this you have already been told, but appears necessary to repeat. Expressions given to `function` are not necessarily evaluated. They will be evaluated if assigned names.
    > 
    > 
    > test(4, zed = is.logical(x < 4) )
    > #[1] ""
    > 
    > The function()-function will parse the contents of the parentheses for number of arguments and for parse()-ability. It will evaluate named arguments created with "=". In the context of parsing the formals of a function the "=" operator is different than the "<-" function.
    > 
    > The substitute function will not evaluate (since in the language of R operations it is "special"), but rather checks that the expression can be parsed by R's rules, i.e. is a valid parse tree. `deparse` returns the original character representation.
    > 
    > -- 
    > 
    > David
    > 
    > 
    >> 
    >> Shelby
    >>  
    >> On 9/6/19, 1:02 PM, "R-help on behalf of Richard M. Heiberger" <r-help-bounces at r-project.org on behalf of rmh at temple.edu> wrote:
    >> 
    >>     You might also want to look at the codetools package, for example the
    >>     showTree function " Prints a Lisp-style representation of R
    >>     expression."
    >>          > library(codetools)
    >>          > showTree(quote(x %*% x))
    >>     (%*% x x)
    >>     > showTree(quote(a+b))
    >>     (+ a b)
    >>     > showTree(quote(y ~ a+b))
    >>     (~ y (+ a b))

        
>>          On Fri, Sep 6, 2019 at 2:30 PM Bert Gunter <bgunter.4567 at gmail.com> wrote:

        
>>     >
    >>     > The following may be of use (it gives the parse tree of the text):
    >>     >
    >>     > > z <- as.list(parse(text = "function(x)x %*% x"))
    >>     > > z[[1]]
    >>     > function(x) x %*% x
    >>     > > z[[c(1,1)]]
    >>     > `function`
    >>     > > z[[c(1,2)]]
    >>     > $x
    >>     > > z[[c(1,3)]]
    >>     > x %*% x
    >>     > > z[[c(1,3,1)]]
    >>     > `%*%`
    >>     > > z[[c(1,3,2)]]
    >>     > x
    >>     > > z[[c(1,3,3)]]
    >>     > x
    >>     >
    >>     >
    >>     > Bert Gunter
    >>     >
    >>     >
    >>     >

        
>>     > On Fri, Sep 6, 2019 at 10:14 AM Wang Jiefei <szwjf08 at gmail.com> wrote:

        
>>     >
    >>     > > If you are looking for an R code parser, I think the `parse` and `eval`
    >>     > > function might be a good start point. See the example below.
    >>     > >
    >>     > > > parse(text="function(x)message(x)")
    >>     > > expression(function(x)message(x))
    >>     > > > eval(parse(text="function(x)message(x)"))
    >>     > > function(x)message(x)
    >>     > >
    >>     > > Best,
    >>     > > Jiefei
    >>     > >
    >>     > > On Fri, Sep 6, 2019 at 12:55 PM Golden, Shelby <GoldenS at njhealth.org>

        
>>     > > wrote:

        
>>     > >
    >>     > >> Hello Bert,
    >>     > >>
    >>     > >> Thank you for the reply and your clarifications. Yes, it might be helpful
    >>     > >> to look into R?s formal grammar to see how ?function? parses input to
    >>     > >> delegate correct syntax. Is that accessible online?
    >>     > >>
    >>     > >> Thank you,
    >>     > >> Shelby
    >>     > >>
    >>     > >>
    >>     > >> From: Bert Gunter <bgunter.4567 at gmail.com>
    >>     > >> Date: Friday, September 6, 2019 at 10:44 AM
    >>     > >> To: "Golden, Shelby" <GoldenS at NJHealth.org>
    >>     > >> Cc: "r-help at R-project.org" <r-help at r-project.org>, "Gillenwater, Lucas" <
    >>     > >> GILLENWATERL at NJHEALTH.ORG>
    >>     > >> Subject: Re: [R] [R-devel] Source Code for function
    >>     > >>
    >>     > >> 1. This is a plain text list; all html is stripped. So there is no red
    >>     > >> highlighting.
    >>     > >>
    >>     > >> 2. There is no "source code" for "function" -- it is a reserved keyword.
    >>     > >> Or are you looking for R's formal grammar -- e.g. how it parses input to
    >>     > >> determine correct syntax?
    >>     > >>
    >>     > >>
    >>     > >>
    >>     > >> Bert Gunter
    >>     > >>
    >>     > >> "The trouble with having an open mind is that people keep coming along
    >>     > >> and sticking things into it."
    >>     > >> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
    >>     > >>
    >>     > >>
    >>     > >> On Fri, Sep 6, 2019 at 8:51 AM Golden, Shelby <GoldenS at njhealth.org

        
>>     > >> <mailto:GoldenS at njhealth.org>> wrote:

        
>>     > >> Hi all,
    >>     > >>
    >>     > >> I have been attempting to access the source code for the keyword
    >>     > >> ?function? to better understand how it assigns and stores logical inputs,
    >>     > >> like in the subset() [base] function. Does anyone know how I can access the
    >>     > >> source code for this?
    >>     > >>
    >>     > >> For example, if I have
    >>     > >> norm <- function(x){
    >>     > >>       sqrt(x%*%x))
    >>     > >> }
    >>     > >> I am looking for the source code for the ?function? portion, highlighted
    >>     > >> in red.
    >>     > >>
    >>     > >> Thank you for your time and assistance,
    >>     > >> Shelby Golden
    >>     > >> Lab Researcher Technician
    >>     > >> Dr. Russell Bowler?s Lab
    >>     > >> Department of Medicine
    >>     > >> National Jewish Health in Denver, CO
    >>     > >> Phone: (303) 270-2598
    >>     > >>
    >>     > >> NOTICE: This email message is for the sole use of the intended
    >>     > >> recipient(s) and may contain confidential and privileged information. Any
    >>     > >> unauthorized review, use, disclosure or distribution is prohibited. If you
    >>     > >> are not the intended recipient, please contact the sender by reply email
    >>     > >> and destroy all copies of the original message.
    >>     > >>         [[alternative HTML version deleted]]
    >>     > >>
    >>     > >> ______________________________________________
    >>     > >> R-help at r-project.org<mailto:R-help at r-project.org> mailing list -- To
    >>     > >> UNSUBSCRIBE and more, see
    >>     > >> https://stat.ethz.ch/mailman/listinfo/r-help<
    >>     > >> http://mx2.njhealth.org:32224/?dmVyPTEuMDAxJiZmMWRiYmMxZjFmNmI5ZDBkMz01RDcyOEQwN18yMjk2OF8zOTk2XzEmJjljNzlmMDA4YWRmZTZjMz0xMjMzJiZ1cmw9aHR0cHMlM0ElMkYlMkZzdGF0JTJFZXRoeiUyRWNoJTJGbWFpbG1hbiUyRmxpc3RpbmZvJTJGci1oZWxw
    >>     > >> >
    >>     > >> PLEASE do read the posting guide
    >>     > >> http://www.R-project.org/posting-guide.html<
    >>     > >> http://mx2.njhealth.org:32224/?dmVyPTEuMDAxJiZlMTkwYmMwMzFlNjk4ZTAzNz01RDcyOEQwN18yMjk2OF8zOTk2XzEmJmFkYTkxMWRkMWRhZTFkNz0xMjMzJiZ1cmw9aHR0cCUzQSUyRiUyRnd3dyUyRVItcHJvamVjdCUyRW9yZyUyRnBvc3RpbmctZ3VpZGUlMkVodG1s
    >>     > >> >
    >>     > >> and provide commented, minimal, self-contained, reproducible code.
    >>     > >>
    >>     > >>         [[alternative HTML version deleted]]
    >>     > >>
    >>     > >> ______________________________________________
    >>     > >> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
    >>     > >> https://stat.ethz.ch/mailman/listinfo/r-help
    >>     > >> PLEASE do read the posting guide
    >>     > >> http://www.R-project.org/posting-guide.html
    >>     > >> and provide commented, minimal, self-contained, reproducible code.
    >>     > >>
    >>     > >
    >>     >
    >>     >         [[alternative HTML version deleted]]
    >>     >
    >>     > ______________________________________________
    >>     > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
    >>     > https://stat.ethz.ch/mailman/listinfo/r-help
    >>     > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
    >>     > and provide commented, minimal, self-contained, reproducible code.
    >>          ______________________________________________
    >>     R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
    >>     https://stat.ethz.ch/mailman/listinfo/r-help
    >>     PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
    >>     and provide commented, minimal, self-contained, reproducible code.
    >>     
    >> 
    >> NOTICE: This email message is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message.
    >> ______________________________________________
    >> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
    >> https://stat.ethz.ch/mailman/listinfo/r-help
    >> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
    >> and provide commented, minimal, self-contained, reproducible code.
    > 
    > ______________________________________________
    > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
    > https://stat.ethz.ch/mailman/listinfo/r-help
    > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
    > and provide commented, minimal, self-contained, reproducible code.
    
    -- 
    Peter Dalgaard, Professor,
    Center for Statistics, Copenhagen Business School
    Solbjerg Plads 3, 2000 Frederiksberg, Denmark
    Phone: (+45)38153501
    Office: A 4.23
    Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com

  
  


  


      

    

    

      
      

        


  

        

      Bert Gunter
    

    

      
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It is time to end these queries and start your homework by consulting the
references you have already been given. Wickham's goes into all of this;
the R Language Definition that ships with R covers all of your questions
and more in detail; and numerous online references and tutorials -- A
search on "what is a promise in R" brings up numerous resources, for
example -- are available.

This list is for help. It is not a substitute for studying on your own.

Cheers,
Bert

        
On Fri, Sep 6, 2019 at 3:15 PM Golden, Shelby <GoldenS at njhealth.org> wrote:

        

            

      
      
      
    

        

      
      
    

            

      
      
      
    

        

      
      
    

            

      
      
      
    

        

      
      
    

            

      
      
      
    

        

      
      
    

            

      
      
      
    

        

      
      
    

        

  
  


  


      

    

    
2 days later

    

      
      

        


  

        

      Richard O'Keefe
    

    

      
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argument

            

      
      
      
    

        
evaluations

The "function" keyword does not take a logical argument.
Let me show you some parallels:

f <- function (x, y) {x+y}          # R
(set! f (lambda (x y) (+ x y)))     ; Scheme
f = (x, y) => { return x+y; };      // Javascript
f = (x, y) => { return x+y; };      // C#, given a suitable declaration for
f
f = (x, y) -> { return x+y; }       // Java, given a suitable declaration
for f.
lambda x y; x+y end -> f;           // Pop-2, older than the others.

In all of these,
  - there is something ('function', 'lambda', '=>', '->') that
    says "here is an anonymous function"
  - there is a list of zero or more parameters
  - there is a body which may contain statements and may also
    return a result.
The keyword in itself does nothing.  The compiler recognises the
construction and generates code for a procedure that is bound to
the environment where it is created, so that it can find variables
other than those in its parameter list.

When it comes to passing parameters to a function, there is
nothing special about logical expressions in any of these languages.

Now there *is* something about functions in R that is special.
The S language (which R is based on) is the only one I am familiar
with that combines two properties:
 - it is an imperative language with side effects to variables
 - it does not evaluate function arguments when they are passed
   but when they are first *used*.
An obvious reason for this is to allow plotting methods to construct
labels from their arguments and to allow model fitting methods to
remember the form of the model.

If you want argument evaluation delayed for any other reason, it is
probably better to pass a function.  See

            

      
      
      
    

        
-- the first argument is a function, not a general expression

            

      
      
      
    

        
-- the second argument is a function, not a general expression
(That is, the argument in question is an expression whose value must
be a function, not an expression to be manipulated *textually* or as
a formula.)

        
On Sat, 7 Sep 2019 at 08:07, Golden, Shelby <GoldenS at njhealth.org> wrote:

        

            

      
      
      
    

        

      
      
    

            

      
      
      
    

        

      
      
    

        

      
      
    

        

  
  


  


      

    

    
1 day later

    

      
      

        


  

        

      Golden, Shelby
    

    

      
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Wow, this is great! Thank you, Richard, for going so in-depth with this explanation.

My ultimate goal is to create a vector that stores logical evaluations to be used later in a function that subsets data. I?ve coded multiple projects, now, that require this kind of sub-setting across multiple unique logical evaluations. So, streamlining the in-put and the out-put is ideal to minimize error and generalize my code.

I will look further into this information to see if it can help me get around using parse(text = )), which, to my understanding, is not a good coding method (https://stackoverflow.com/questions/1743698/evaluate-expression-given-as-a-string - comment left Martin Maechler).

Thank you again, and I hope you have a wonderful week!

Shelby


From: Richard O'Keefe <raoknz at gmail.com>
Date: Sunday, September 8, 2019 at 11:01 PM
To: "Golden, Shelby" <GoldenS at NJHealth.org>
Cc: "Richard M. Heiberger" <rmh at temple.edu>, Bert Gunter <bgunter.4567 at gmail.com>, "r-help at R-project.org" <r-help at r-project.org>, "Gillenwater, Lucas" <GILLENWATERL at NJHEALTH.ORG>
Subject: Re: [R] [R-devel] Source Code for function

            

      
      
      
    

        
The "function" keyword does not take a logical argument.
Let me show you some parallels:

f <- function (x, y) {x+y}          # R
(set! f (lambda (x y) (+ x y)))     ; Scheme
f = (x, y) => { return x+y; };      // Javascript
f = (x, y) => { return x+y; };      // C#, given a suitable declaration for f
f = (x, y) -> { return x+y; }       // Java, given a suitable declaration for f.
lambda x y; x+y end -> f;           // Pop-2, older than the others.

In all of these,
  - there is something ('function', 'lambda', '=>', '->') that
    says "here is an anonymous function"
  - there is a list of zero or more parameters
  - there is a body which may contain statements and may also
    return a result.
The keyword in itself does nothing.  The compiler recognises the
construction and generates code for a procedure that is bound to
the environment where it is created, so that it can find variables
other than those in its parameter list.

When it comes to passing parameters to a function, there is
nothing special about logical expressions in any of these languages.

Now there *is* something about functions in R that is special.
The S language (which R is based on) is the only one I am familiar
with that combines two properties:
 - it is an imperative language with side effects to variables
 - it does not evaluate function arguments when they are passed
   but when they are first *used*.
An obvious reason for this is to allow plotting methods to construct
labels from their arguments and to allow model fitting methods to
remember the form of the model.

If you want argument evaluation delayed for any other reason, it is
probably better to pass a function.  See

            

      
      
      
    

        
-- the first argument is a function, not a general expression

            

      
      
      
    

        
-- the second argument is a function, not a general expression
(That is, the argument in question is an expression whose value must
be a function, not an expression to be manipulated *textually* or as
a formula.)

        
On Sat, 7 Sep 2019 at 08:07, Golden, Shelby <GoldenS at njhealth.org<mailto:GoldenS at njhealth.org>> wrote:

        
Thank you all for your reply. I should clarify, that I am looking to understand why the keyword function can take a logical argument (eg: x<4) and use that later inside the function's definition for logical evaluations.

Consider this example, which is a simplification of getAnywhere(subset.data.frame):
x = data.frame("Col1" = c(1, 2, 3, 4, 5), "Col2" = c(6, 7, 8, 9, 10))
test <- function(x, logic){
        e <- substitute(logic)
        r <- eval(e, x, parent.frame())
        r[r]
}


Shelby

        
On 9/6/19, 1:02 PM, "R-help on behalf of Richard M. Heiberger" <r-help-bounces at r-project.org<mailto:r-help-bounces at r-project.org> on behalf of rmh at temple.edu<mailto:rmh at temple.edu>> wrote:

        
You might also want to look at the codetools package, for example the
    showTree function " Prints a Lisp-style representation of R
    expression."

    > library(codetools)

    > showTree(quote(x %*% x))
    (%*% x x)
    > showTree(quote(a+b))
    (+ a b)
    > showTree(quote(y ~ a+b))
    (~ y (+ a b))

        
On Fri, Sep 6, 2019 at 2:30 PM Bert Gunter <bgunter.4567 at gmail.com<mailto:bgunter.4567 at gmail.com>> wrote:

        
>
    > The following may be of use (it gives the parse tree of the text):
    >
    > > z <- as.list(parse(text = "function(x)x %*% x"))
    > > z[[1]]
    > function(x) x %*% x
    > > z[[c(1,1)]]
    > `function`
    > > z[[c(1,2)]]
    > $x
    > > z[[c(1,3)]]
    > x %*% x
    > > z[[c(1,3,1)]]
    > `%*%`
    > > z[[c(1,3,2)]]
    > x
    > > z[[c(1,3,3)]]
    > x
    >
    >
    > Bert Gunter
    >
    >
    >

        
> On Fri, Sep 6, 2019 at 10:14 AM Wang Jiefei <szwjf08 at gmail.com<mailto:szwjf08 at gmail.com>> wrote:

        
>
    > > If you are looking for an R code parser, I think the `parse` and `eval`
    > > function might be a good start point. See the example below.
    > >
    > > > parse(text="function(x)message(x)")
    > > expression(function(x)message(x))
    > > > eval(parse(text="function(x)message(x)"))
    > > function(x)message(x)
    > >
    > > Best,
    > > Jiefei
    > >
    > > On Fri, Sep 6, 2019 at 12:55 PM Golden, Shelby <GoldenS at njhealth.org<mailto:GoldenS at njhealth.org>>

        
> > wrote:

        
> >
    > >> Hello Bert,
    > >>
    > >> Thank you for the reply and your clarifications. Yes, it might be helpful
    > >> to look into R?s formal grammar to see how ?function? parses input to
    > >> delegate correct syntax. Is that accessible online?
    > >>
    > >> Thank you,
    > >> Shelby
    > >>
    > >>
    > >> From: Bert Gunter <bgunter.4567 at gmail.com<mailto:bgunter.4567 at gmail.com>>
    > >> Date: Friday, September 6, 2019 at 10:44 AM
    > >> To: "Golden, Shelby" <GoldenS at NJHealth.org>
    > >> Cc: "r-help at R-project.org" <r-help at r-project.org<mailto:r-help at r-project.org>>, "Gillenwater, Lucas" <
    > >> GILLENWATERL at NJHEALTH.ORG<mailto:GILLENWATERL at NJHEALTH.ORG>>
    > >> Subject: Re: [R] [R-devel] Source Code for function
    > >>
    > >> 1. This is a plain text list; all html is stripped. So there is no red
    > >> highlighting.
    > >>
    > >> 2. There is no "source code" for "function" -- it is a reserved keyword.
    > >> Or are you looking for R's formal grammar -- e.g. how it parses input to
    > >> determine correct syntax?
    > >>
    > >>
    > >>
    > >> Bert Gunter
    > >>
    > >> "The trouble with having an open mind is that people keep coming along
    > >> and sticking things into it."
    > >> -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
    > >>
    > >>
    > >> On Fri, Sep 6, 2019 at 8:51 AM Golden, Shelby <GoldenS at njhealth.org<mailto:GoldenS at njhealth.org>

        
> >> <mailto:GoldenS at njhealth.org<mailto:GoldenS at njhealth.org>>> wrote:

        
> >> Hi all,
    > >>
    > >> I have been attempting to access the source code for the keyword
    > >> ?function? to better understand how it assigns and stores logical inputs,
    > >> like in the subset() [base] function. Does anyone know how I can access the
    > >> source code for this?
    > >>
    > >> For example, if I have
    > >> norm <- function(x){
    > >>       sqrt(x%*%x))
    > >> }
    > >> I am looking for the source code for the ?function? portion, highlighted
    > >> in red.
    > >>
    > >> Thank you for your time and assistance,
    > >> Shelby Golden
    > >> Lab Researcher Technician
    > >> Dr. Russell Bowler?s Lab
    > >> Department of Medicine
    > >> National Jewish Health in Denver, CO
    > >> Phone: (303) 270-2598
    > >>
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and provide commented, minimal, self-contained, reproducible code.

  
  


  


      

    

    

      
      

        


  

        

      David Winsemius
    

    

      
      #
    

  


  

      
On 9/10/19 11:13 AM, Golden, Shelby wrote:

            

      
      
      
    

        
It appears you have in mind keeping around a set of "off-the-shelf" 
expressions that will be chosen for varying situations. It seems to me 
that you should instead be storing complex predefined logical 
constructions in functions that can be applied to multi-column objects 
like dataframes, data.tables, or matrices:


 > A_is_GT_B <- function(A, B){ A > B}
 > set.seed(123)
 > test <- data.frame(x=sample(10),y=sample(10), z=sample(10) )
 > test$x_GT_y <- with(test, A_is_GT_B(x,y))
 > test
 ??? x? y? z x_GT_y
1?? 3 10? 8? FALSE
2? 10? 5? 7?? TRUE
3?? 2? 3? 2? FALSE
4?? 8? 8? 1? FALSE
5?? 6? 1? 6?? TRUE
6?? 9? 4? 3?? TRUE
7?? 1? 6? 4? FALSE
8?? 7? 9 10? FALSE
9?? 5? 7? 9? FALSE

10? 4? 2? 5?? TRUE

The expressions then are encapsulated inside the function and you can 
make lists that carry multiple functions.

It does remain possible to have expression vectors:

exprs <- expression( x > y, x >+ z)

eval( exprs[[2]], test)

 > exprs <- expression( x > y, x >+ z)
 >
 > eval( exprs[[2]], test)
 ?[1] FALSE? TRUE FALSE? TRUE FALSE? TRUE FALSE FALSE FALSE FALSE


This however is considered poor practice. Notice that you are 
constrained to know ahead of time the column names of the arguments to 
be passed, whereas with the function-approach, the names are not 
required and you can use positional matching.