How to search an environment using ls() inside a function?

Question

I want to find a set of functions and save them, because I want to send them to a remote server in an Rdata file, and I don't want to install a new package on the server.

Although I am getting an error using the approach below, easier / better approaches are welcome.

MWE:

Here are two dummy functions:

abcd.fun.1    <- function() return(1)
abcd.fun.2    <- function() return(2)

I can identify the dummy functions:

ls()[grep('abcd', ls())]

But when I wrap this in a function:

 find.test <- function(x) {
     return(ls()[grep(x, ls())])
 }
 find.test('abcd')

The function returns character(0)

Ultimately I would like to

 save(find.test('abcd'), file = test.Rdata)

score 12 · Accepted Answer · answered Nov 15 '11 at 20:54

12

Why not use the pattern= argument to ls?
Calling ls inside a function lists the objects that exist within the function scope, not the global environment (this is explained in ?ls).

If you want to list the objects in the global environment from a function, specify envir=.GlobalEnv.

x <- 1:10
f <- function() ls()
g <- function() ls(envir=.GlobalEnv)
h <- function() ls(envir=.GlobalEnv, pattern="[fg]")
f()
# character(0)
g()
# [1] "f" "g" "h" "x"
h()
# [1] "f" "g"

answered Nov 15 '11 at 20:54

Joshua Ulrich

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globalenv() is preferred these days – hadley Nov 16 '11 at 03:13
@hadley: could you explain why? – Joshua Ulrich Nov 16 '11 at 13:09
Hmmm, I could've sworn it suggested that in the documentation but I guess not. In that case it's just personal opinion: I think it's nicer to use a function than a global. – hadley Nov 16 '11 at 13:59

score 7 · Answer 2 · answered Nov 15 '11 at 20:56

You need to tell your function to list objects in an environment other than itself, e.g. the global environment. (And while you're at it, you can also specify the regex pattern as an argument to ls.):

find.test <- function(x, envir=.GlobalEnv) {
  ls(pattern=x, envir=envir) 
}

See ?ls for more info about ls() and ?environment for other options to specify the environment.

How to search an environment using ls() inside a function?

2 Answers2

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