get() within function

  
Hi Ivan,

ls() inside a function gives you the variables in the local scope. If you want to get the variables defined in the global scope you need to tell ls() that.

Check the difference between these three functions:

foo <- function() ls()
foo()

Returns character(0) because there are no local variables.

bar <- function(x) ls()
bar(1)

Returns ?x? because ls() sees the function parameter

baz <- function() ls(envir = .GlobalEnv)
baz()

Returns all the variables in the global environment.

If you change your function foo() to this, it should work:


foo <- function() {
   selected_names <- sapply(ls(.GlobalEnv),
                            function(x) class(get(x))) %in% c("data.frame","list")
   df.list <- ls(.GlobalEnv)[selected_names]
   dat.str <- select.list(choices=df.list, title="Select object")
   dat <- get(dat.str)
   str(dat)
}

Cheers
	Thomas






On 18 August 2016 at 12:21:33, Ivan Calandra (ivan.calandra at univ-reims.fr(mailto:ivan.calandra at univ-reims.fr)) wrote:

Dear useRs,
  
For an interactive use, I am trying to write a function that looks for
all data.frames and lists in the environment and ask the user to select
one of them. I then run some operations on this object.
  
This is what I am trying:
  
foo <- function(){
df.list <- ls()[sapply(ls(), function(x) class(get(x))) %in%
c("data.frame","list")]
dat.str <- select.list(choices=df.list, title="Select object")
dat <- get(dat.str)
str(dat)
}
  
Let's say I have these three objects:
vec <- 1:10
mylist <- list(1:3)
datf <- data.frame(var1=rnorm(10), var2=rnorm(10))
  
I would like the function to show me only mylist and datf in the dialog
box. Everything works fine if I take the code out of the function, but
when I run foo() I get this error:
"Error in get(dat.str) : first argument incorrect"
  
Is there a problem with using get() within a function? Maybe a problem
with environments?
  
Thank you in advance for any help!
Ivan
  
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ivan.calandra at univ-reims.fr
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