passing arguments to subset from a function

Available free for the typing are the functions for the default and  
the dataframe methods of subset:

 >  subset.default
function (x, subset, ...)
{
     if (!is.logical(subset))
         stop("'subset' must be logical")
     x[subset & !is.na(subset)]
}


 > subset.data.frame
function (x, subset, select, drop = FALSE, ...)
{
     if (missing(subset))
         r <- TRUE
     else {
         e <- substitute(subset)
         r <- eval(e, x, parent.frame())
         if (!is.logical(r))
             stop("'subset' must evaluate to logical")
         r <- r & !is.na(r)
     }
     if (missing(select))
         vars <- TRUE
     else {
         nl <- as.list(1:ncol(x))
         names(nl) <- names(x)
         vars <- eval(substitute(select), nl, parent.frame())
     }
     x[r, vars, drop = drop]
}

(There is also a matrix method.)

David Winsemius


On Dec 17, 2008, at 2:07 PM, GOUACHE David wrote:

> Hello R-helpers,
>
> I'm writing a long function in which I manipulate a certain number  
> of datasets. I want the arguments of said function to allow me to  
> adapt the way I do this. Among other things, I want my function to  
> have an argument which I will pass on to subset() somewhere inside  
> my function. Here is a quick and simplified example with the iris  
> dataset.
>
> myfunction<-function(table, extraction)  {
>     table2<-subset(table, extraction)
> return(table2) }
>
> myfunction(iris, extraction= Species=="setosa")
>
>
> ############## end
>
> What I would like is for this function to return exactly the same  
> thing as :
> subset(iris, Species=="setosa")
>
>
> Thanks for your help.
>
> Regards,
>
> David Gouache
>
> ______________________________________________
> R-help at r-project.org mailing list
> 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.

I wrote a dirty hack last time I faced this problem, I'll be curious  
to see what is the proper way of dealing with the scoping and  
evaluation rules.

library(datasets)

myfunction<-function(table, extraction)  {
     table2<-subset(table,extraction)
return(table2)
}


condition1 <- quote(iris$Species=="setosa") # I'm not sure how to  
evaluate within the environment, perhaps you could use with(table,  
subset(table, extraction) ) in your function
condition2 <- bquote(.(condition1)  & iris$Sepal.Width < 3.5) # say,  
if you want to concatenate several conditions together

myfunction(iris, extraction= eval(condition1))
myfunction(iris, extraction= eval(condition2))


Best wishes,

baptiste

Hello R-helpers,

I'm writing a long function in which I manipulate a certain number  
of datasets. I want the arguments of said function to allow me to  
adapt the way I do this. Among other things, I want my function to  
have an argument which I will pass on to subset() somewhere inside  
my function. Here is a quick and simplified example with the iris  
dataset.

myfunction<-function(table, extraction)  {
    table2<-subset(table, extraction)
return(table2) }

myfunction(iris, extraction= Species=="setosa")


############## end

What I would like is for this function to return exactly the same  
thing as :
subset(iris, Species=="setosa")


Thanks for your help.

Regards,

David Gouache

______________________________________________
R-help at r-project.org mailing list
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.

_____________________________

Baptiste Augui?

School of Physics
University of Exeter
Stocker Road,
Exeter, Devon,
EX4 4QL, UK

Phone: +44 1392 264187

http://newton.ex.ac.uk/research/emag

This thread may help?

https://stat.ethz.ch/pipermail/r-help/2007-November/145345.html

On Wed, 17 Dec 2008 20:07:08 +0100, "GOUACHE David"

Hello R-helpers,

I'm writing a long function in which I manipulate a certain number of
datasets. I want the arguments of said function to allow me to adapt the
way I do this. Among other things, I want my function to have an argument
which I will pass on to subset() somewhere inside my function. Here is a
quick and simplified example with the iris dataset.

myfunction<-function(table, extraction)  {
     table2<-subset(table, extraction)
return(table2) }

myfunction(iris, extraction= Species=="setosa")


############## end

What I would like is for this function to return exactly the same thing

as

:
subset(iris, Species=="setosa")


Thanks for your help.

Regards,

David Gouache

______________________________________________
R-help at r-project.org mailing list
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.

argument which I will pass on to subset() somewhere inside my function.  

I would use the example of .() function from plyr package in this case:

.<-function (...){
     structure(as.list(match.call()[-1]), class = "quoted")
}

myfunction<-function(table, extraction)  {
     table2<-subset(table, eval(extraction[[1]]))
     return(table2)
 }
myfunction(iris, extraction = .(Species=="setosa"))

You can pass as many arguments in .() as you wish and index correspondingly in myfunction afterwards.

HTH.