[R] Extracting a (*specific*) variable name from a list of function arguments (not "...")

[Uwe Ligges]

On 30.01.2011 17:38, Tal Galili wrote:
> Hello all,
>
> I would like to extract the variable name passed into a specific argument of
> a function.
> Using match.call() will give me a list of arguments and what was passed into
> them, but I couldn't find how to get a particular argument out of it (at
> least without using some string manipulation).
>
> Here is an example (in it, my objective is to know what is the variable name
> assigned to the argument "b"):
>
> foo<- function(a, b, c)
> {
> print(match.call())

Replace by

   print(substitute(b))

Uwe Ligges


> }
> x = 1 ; y = 1
> foo(x, y)  # here the answer should be "y"
> foo(c= x, y)  # here the answer should be "" (or NULL/NA)
>
>
> Any suggestion on how to do this?
>
>
> BTW, the purpose of this is to be able to avoid the error produced by, for
> example, this:
>
> yy<- data.frame(y = 1:10, x = 1:10)
> plot(y, data = yy) # error
> plot(y~x, data = yy) # no error...
>
>
>
>
> Thanks,
> Tal
>
>
>
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