[R] Using names in function with ellipsis (non standard evaluation?)
Luca Cerone
luca.cerone at gmail.com
Fri May 29 05:35:16 CEST 2015
Thanks a lot to all of you for the help!
Duncan's solution is what I was looking for!
In my examples I assumed that if f(...) is called by g then the names
I use in g were transferred to f, which is not true.
But calling f as Duncan explained ( g <- function(x,y) f(x=x,y=y) )
solves the issue!
Thanks a lot again for helping me with this!
Cheers,
Luca
On Thu, May 28, 2015 at 10:49 PM, Bert Gunter <bgunter.4567 at gmail.com> wrote:
> I also am not sure exactly what the OP wants and even less sure of what he
> needs...
>
> But a possible answer is that a canonical way to do this is just to pass
> down the ... list in the definition and specifying a named list of arguments
> in the call (as has already been mentioned).
>
> e.g. consider:
>
>> g <- function(f,...)f(...)
> ## so g can accept arbitrary functions with arbitrary arguments
>
>> fru <- function(x,y=3)x+y
>
>> g(fru,x=2) ## default y used
> [1] 5
>
>> g(fru,x=2,y=7) ## y argument given explicitly
> [1] 9
>
>
> Please pardon the noise if this is irrelevant.
>
> Cheers,
> Bert
>
> On Thu, May 28, 2015 at 12:17 PM, Duncan Murdoch <murdoch.duncan at gmail.com>
> wrote:
>>
>> On 28/05/2015 1:40 PM, Luca Cerone wrote:
>> > Hi everybody,
>> >
>> > this is probably a silly question, but I can't find a way to recognize
>> > the names that are passed
>> > to variables in ellipsis.
>> >
>> > For example, say I have a "core" function that receives some extra
>> > parameters through ...
>> > e.g.
>> >
>> > f <- function(...) {
>> > params <- c(...)
>> > #dothehardworkhere using "names(params)"
>> > }
>> >
>> > and then I want to create a function g where some of the parameters
>> > are set like:
>> >
>> > g <- function(x,y) f(x,y)
>> >
>> > I figure I probably have to use to substitute in f, but it is not
>> > clear to me how.
>> >
>> > Definitely what I need to achieve is that when I call:
>> >
>> > g(1,2) then in f params is the vector c(x=1,y=2);
>> > similarly I want to be able to call g(y=2, x=1)
>> > and have params = c(x=1,y=2) in f.
>> >
>> > Can you please help me understanding how to do this?
>>
>> Sorry, I misunderstood your question. I didn't notice that g calls f.
>> You should write g to call f with names on the parameters, i.e.
>>
>> g <- function(x,y) f(x=x, y=y)
>>
>> then f will receive the parameters with names on them. I'd still advise
>> against using c(...), but it will give you the output you want with that
>> input; the problem is if your users do something like
>> g(1:2, 3:4) (which would give c(x1=1, x2=2, y1=3, y2=4)).
>>
>> Duncan Murdoch
>>
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>
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