R help - Aug 2012 - Extracting the name of a function (inverse of match.fun("myFun"))

Hi all,

is there a way to extract the name of a function, i.e. do the reverse
of match.fun applied to a character string? I would like to print out
the name of a function supplied to another function as an argument.

For example:

myFunc = function(x) { x+1 }

applyFunc = function(fnc, x)
{
  fnc = match.fun(fnc)
  fnc(x)
}

Is there a way to obtain "myFunc" from the argument fnc in applyFnc
the following call is issued?

applyFnc(myFunc, 1)



Thanks,

Peter

On Wed, Aug 29, 2012 at 3:36 PM, Peter Langfelder
<peter.langfelder at gmail.com> wrote:
> Hi all,
>
> is there a way to extract the name of a function, i.e. do the reverse
> of match.fun applied to a character string? I would like to print out
> the name of a function supplied to another function as an argument.
>
> For example:
>
> myFunc = function(x) { x+1 }
>
> applyFunc = function(fnc, x)
> {
>   fnc = match.fun(fnc)
>   fnc(x)
> }
>
> Is there a way to obtain "myFunc" from the argument fnc in
applyFnc
> the following call is issued?
>
> applyFnc(myFunc, 1)
...or am I missing the basic fact that since arguments to functions in
R are passed by copy, the name is lost/meaningless?

Thanks,

Peter

On 12-08-29 04:00 PM, Peter Langfelder wrote:
> On Wed, Aug 29, 2012 at 3:36 PM, Peter Langfelder
> <peter.langfelder at gmail.com> wrote:
>> Hi all,
>>
>> is there a way to extract the name of a function, i.e. do the reverse
>> of match.fun applied to a character string? I would like to print out
>> the name of a function supplied to another function as an argument.
>>
>> For example:
>>
>> myFunc = function(x) { x+1 }
>>
>> applyFunc = function(fnc, x)
>> {
>>    fnc = match.fun(fnc)
>>    fnc(x)
>> }
>>
>> Is there a way to obtain "myFunc" from the argument fnc in
applyFnc
>> the following call is issued?
>>
>> applyFnc(myFunc, 1)
> ...or am I missing the basic fact that since arguments to functions in
> R are passed by copy, the name is lost/meaningless?
You can pass the function name as a string.

applyFunc = function(fun, x)
{
   fnc = match.fun(fun)
    fnc(x)
    print(fun)
}

applyFunc("myFunc", 1)
[1] "myFunc"

PS : avoid renaming the name of your argument within the function ("fnc 
= match.fun(fnc)").

Cheers,

Eloi
>
> Thanks,
>
> Peter
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
>

-- 
Eloi Mercier
Bioinformatics PhD Student, UBC
Paul Pavlidis Lab
2185 East Mall
University of British Columbia
Vancouver BC V6T1Z4

deparse(substitute(fnc)) will get you part way there.

myFunc <- function(x) x + 1
applyFunc <- function(fnc, x) {
    cat("fnc is", deparse(substitute(fnc)), "\n")
    fnc <- match.fun(fnc)
    fnc(x)
}
> applyFunc(myFunc, 1:3)
fnc is myFunc
[1] 2 3 4
> applyFunc(function(x)x*10, 1:3)
fnc is function(x) x * 10
[1] 10 20 30
> applyFunc("myFunc", 1:3)
fnc is "myFunc"
[1] 2 3 4

I like to let the user override what substitute might say by
making a new argument out of it:
> applyFunc(function(x)x*10, 1:3)
fnc is function(x) x * 10
[1] 10 20 30
> applyFunc(function(x)x*10, 1:3, fncString="Times 10")
fnc is Times 10
[1] 10 20 30
This makes is easier to call your function from another one - you
can pass the fncString down through a chain of calls.

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at
r-project.org] On Behalf
> Of Peter Langfelder
> Sent: Wednesday, August 29, 2012 4:00 PM
> To: r-help
> Subject: Re: [R] Extracting the name of a function (inverse of
match.fun("myFun"))
> 
> On Wed, Aug 29, 2012 at 3:36 PM, Peter Langfelder
> <peter.langfelder at gmail.com> wrote:
> > Hi all,
> >
> > is there a way to extract the name of a function, i.e. do the reverse
> > of match.fun applied to a character string? I would like to print out
> > the name of a function supplied to another function as an argument.
> >
> > For example:
> >
> > myFunc = function(x) { x+1 }
> >
> > applyFunc = function(fnc, x)
> > {
> >   fnc = match.fun(fnc)
> >   fnc(x)
> > }
> >
> > Is there a way to obtain "myFunc" from the argument fnc in
applyFnc
> > the following call is issued?
> >
> > applyFnc(myFunc, 1)
> 
> ...or am I missing the basic fact that since arguments to functions in
> R are passed by copy, the name is lost/meaningless?
> 
> Thanks,
> 
> Peter
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

On 30/08/12 10:36, Peter Langfelder wrote:
> Hi all,
>
> is there a way to extract the name of a function, i.e. do the reverse
> of match.fun applied to a character string? I would like to print out
> the name of a function supplied to another function as an argument.
>
> For example:
>
> myFunc = function(x) { x+1 }
>
> applyFunc = function(fnc, x)
> {
>    fnc = match.fun(fnc)
>    fnc(x)
> }
>
> Is there a way to obtain "myFunc" from the argument fnc in
applyFnc
> the following call is issued?
>
> applyFnc(myFunc, 1)
You can just do:

applyFunc = function(fnc, x)
{
   fnc(x)
}

You don't need to get the function's name.

That being said, you seem basically to be re-inventing do.call() in a 
rather kludgy
way.  I would advise you to think carefully through what you are trying 
to accomplish.

     cheers,

         Rolf Turner

P. S. If you really want to get the *name* of the argument "fnc", you 
can use
good old deparse(substitute(...)).  As in:

     fname <- deparse(substitute(fnc))

But as I said, you don't need to do this for what seems to be your purpose,
and so it's all rather off the point.

         R. T.

On Wed, Aug 29, 2012 at 4:14 PM, William Dunlap <wdunlap at tibco.com>
wrote:
> deparse(substitute(fnc)) will get you part way there.
...
> I like to let the user override what substitute might say by
> making a new argument out of it:
>> applyFunc(function(x)x*10, 1:3)
> fnc is function(x) x * 10
> [1] 10 20 30
>> applyFunc(function(x)x*10, 1:3, fncString="Times 10")
> fnc is Times 10
> [1] 10 20 30
> This makes is easier to call your function from another one - you
> can pass the fncString down through a chain of calls.
Thanks, very good suggestions. The function I am writing is of course
much more complicated than the simplistic example.

Peter