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

[Michael Weylandt]

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.
> 
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