[R] Trying to build up functions with its names by means of lapply

[Rui Barradas]

Hello,

My solution works but it is incorrect. We should force the argument 'c', 
not the return value. Like said in the help page for force. Which I've 
only read after my first post. The following way makes much more sense 
and is a bit shorter.

faux <- function(c) {
	force(c)
	function (x) get(paste0(c,"gamma"))(x,k,scale=theta)
}

Rui Barradas

Em 05-06-2013 10:49, Rui Barradas escreveu:
> Hello,
>
> If in faux we ?force the return value, the bug is gone.
>
>
> faux <- function(c) {
>      f <- function (x) get(paste0(c,"gamma"))(x,k,scale=theta)
>      force(f)
>      f
> }
>
> Hope this helps,
>
> Rui Barradas
>
> Em 05-06-2013 07:13, Michael Weylandt escreveu:
>>
>>
>> On Jun 5, 2013, at 3:53, Julio Sergio <juliosergio at gmail.com> wrote:
>>
>>> I want to generate specific gamma distribution functions, given fixed
>>> parameters.
>>> This is I have k, and theta, say
>>>
>>>    k <- 32.2549       # shape
>>>    theta <- 26.32809  # scale
>>>
>>>
>>>    # I have an auxiliary function that produces funcions according to
>>>    # a given character (this is to have either dgamma, pgamma or qgamma)
>>>    # for the specific parameters given above:
>>>
>>>    faux <- function(c) {
>>>      function (x) get(paste0(c,"gamma"))(x,k,scale=theta)
>>>    }
>>>
>>>    # So I can have, for instance, dgamma, and pgamma with
>>>
>>>    dff <- faux("d")
>>>    pff <- faux("p")
>>>
>>>    dff(1000)
>>>    ## [1] 0.001433138
>>>
>>>    pff(1000)
>>>    ## [1] 0.844305
>>>
>>> Now, if I try to produce both functions in one shot with lapply, the
>>> thing
>>> doesn't work, see
>>>
>>>    ffs <- lapply(c("d", "p"), faux)
>>>
>>>    ffs[[1]](1000)
>>>    ## [1] 0.844305
>>>
>>>    ffs[[2]](1000)
>>>    ## [1] 0.844305
>>>
>>> The two produced functions are the very same and correspond to pgamma!!
>>> Maybe I'm missing something. Do you have any idea?
>>
>> I think you are hitting a bit of strangeness R generously calls 'lazy
>> evaluation'.  I'm afraid I don't have a reference at hand, but search
>> the archives for mention of the promise mechanism.
>>
>> MW
>>
>>>
>>> Thanks,
>>>
>>>   -Sergio.
>>>
>>> ______________________________________________
>>> 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.
>>
>> ______________________________________________
>> 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.
>>
>
> ______________________________________________
> 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.