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Create variable by name

7 messages · Ralf B, Peter Langfelder, Jeffrey Spies +2 more

Original
Ralf B
# 
Can one create a variable through a function by name

createVariable <- function(name) {
	outputVariable = name
	name <- NULL
}

after calling

createVariable("myVar")

I would like to have a variable myVar initialized with NULL in my
environment. Is this possible?

Ralf
Peter Langfelder
#
On Wed, Oct 6, 2010 at 9:32 AM, Ralf B <ralf.bierig at gmail.com> wrote:
A clean solution is to use the function assign where you can specify
the environment more precisely.

look at ?assign

Peter
Jeffrey Spies
# 
An alternative to Peter's solution:

createVariable <- function(name) {assign(name, NULL, envir=.GlobalEnv)}

Jeff.
On Wed, Oct 6, 2010 at 12:32 PM, Ralf B <ralf.bierig at gmail.com> wrote:
David Winsemius
#
On Oct 6, 2010, at 12:32 PM, Ralf B wrote:

            

      
      
      
    

        
Isn't that what "<-" does?

            

      
      
      
    

        
?assign   # and isn't this covered in R-FAQ?
?"<-"

 > "myVar" <- NULL
 > myVar
NULL

Doing it a bit differently"

 > "<-"("n1", NULL)
 > n1
NULL

One could always wrap it in a function call.

 > CVN <- function(name) { name <- NULL }
 > CVN("test")
 > test
NULL

If you needed a function that by default created the variable in the  
global environment, then this would work:

 > createGVarNULL <- function(name) {
+ 	assign(name, NULL, envir = .GlobalEnv) }
 > createGVarNULL("test")
 > test
NULL

An "assign" version of "<<-" I suppose.

"myVar" <- NULL
 > myVar
NULL

            

      
      
      
    

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      David Winsemius
    

    

      
      #
    

  


  

      
On Oct 6, 2010, at 12:58 PM, David Winsemius wrote:

        

            

      
      
      
    

        
Perhaps the fastest method would be to use back ticks:

 > cvn <- `<-`  # assign "assign" to a new name, "cvn"
 > cvn("n2", NULL)
 > n2
NULL

            

      
      
      
    

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Greg Snow
    

    

      
      #
    

  


  

      
Possible? Yes (as others have shown), advisable? No, see fortune(106), fortune(236), and possibly fortune(181).

What is your ultimate goal? Maybe we can help you find a better way.

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Ralf B
    

    

      
      #
    

  


  

      
Hi all,

I have scripts that have one variable called 'output', the script
creates a data frame and stores this data frame in 'output'. Then
the data frame is written to disk. This is simple when working with a
single script. However, as soon as one script calls other, variables
overwrite each other.

Here a little example that fixes the problem for one particular case
by using variables with different names:


#
# Script A, either called directly or from another script
#
outputA <- NULL
getOutput <- function(){
      return(outputA)
}
outputA <- "script A"

#
# Script B, includes and executes script A as part of its own
#
output <- NULL
output <- "Script B"
source("C:/data/poodle/coder/overwritingTest/scriptA.R")
outputA <- getOutput()
print(paste("Output script B:", output))
print(paste("Output script A:", outputA ))

However, I simply want to ensure that script A's output does not interfere with
the the one produced by script B without script B's need to know how A called
its variable. I want script B to easily access the output of script A.
What I would
ideally need ( I think) is an OO approach. I was thinking that I could perhaps
store a generic variable that is generated based on the script name
(i.e. scriptA_output, scriptB_output)

        
On Wed, Oct 6, 2010 at 1:24 PM, Greg Snow <Greg.Snow at imail.org> wrote: