global variable in R function

Question

I created a function for processing some of my data, like this:

a <- "old" 
test <- function (x) {
   assign(x, "new", envir = .GlobalEnv)
} 
test(a)

But I can't see the a change from "old" to "new", I guess this is some of the "global variable", any suggestion?

Thanks!

First of all, don't do it -- messing in a global environment with functions is almost always a bad idea leading to random overwrites, hard to track bugs and overall chaos. — mbq
– mbq, Commented Sep 4, 2010 at 8:46

alan · Accepted Answer · 2010-09-04 08:28:40Z

7

for assign(x,value),x need to be a name of a variable not value of it, so x should be in character form: assign("a","new"),and in order to be used in your function,try:

test <- function (x) 
{
  assign(deparse(substitute(x)), "new", envir = .GlobalEnv)
}

in your case, you will creat a variable named "old" and assign "new" to it:

> old
[1] "new"

answered Sep 4, 2010 at 8:28

alan

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Comments

mropa · Accepted Answer · 2010-09-06 14:05:51Z

2

you could combine your function with the sapply function, eg:

require (plyr)
b <- sapply (a, test)
b
  old 
"new"

that way you are applying your function to the actual elements of your a vector - as romunov pointed out in his answer.

another eg:

a <- c("old", "oold", "ooold", "oooold")
b <- sapply (a, test)
b
   old   oold  ooold oooold 
 "new"  "new"  "new"  "new"

edited Sep 6, 2010 at 14:05

answered Sep 4, 2010 at 5:26

mropa

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2 Comments

hatmatrix Over a year ago

which one is the plyr function?

mropa Over a year ago

@Stephen: oh yeah, right. sapply is from the base package - corrected that. the plyr function are always named with one 'p'.

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