[R] Defining functions inside loops

Tue Feb 15 16:53:41 CET 2011

Thanks... but I guess I didn't make myself clear. What I was trying to
do was precisely to "store" inside the function the number associated
to s[i] rather than the call to s[i], such that I wouldn't need to
keep that object in subsequent function calls.

In other words, I wanted to use lapply to get functions equivalent to:
s <- c( 0.2, 0.45, 0.38, 0.9)
f <-list()
f[[1]] <- function(x) x^2+0.2
f[[2]] <- function(x) x^2+0.45
f[[3]] <- function(x) x^2+0.38
f[[4]] <- function(x) x^2+0.9

Best regards,

Eduardo

On Tue, Feb 15, 2011 at 7:20 AM, Dennis Murphy <djmuser at gmail.com> wrote:
> Hi:
>
> If you look at the error message, you'll see that you removed s before
> evaluating f, and since an element of s is called in the function....
>
> Try
>> s <- c( 0.2, 0.45, 0.38, 0.9)
>> f  <- lapply(1:10, function(i)local({ force(i) ; function(x)x^2+s[i]}))
>> f[[1]](s)
> [1] 0.2400 0.4025 0.3444 1.0100
>
> f is a list with 10 components, the first of which is
> [[1]]
> function (x)
> x^2 + s[i]
> <environment: 0x0000000002a26d48>
>
> Each component occupies a different environment. To see what you get,
>
>> f[[1]](0.1)
> [1] 0.21
>
>> for(i in 1:10) print(f[[i]](i))
> [1] 1.2
> [1] 4.45
> [1] 9.38
> [1] 16.9
> [1] NA
> [1] NA
> [1] NA
> [1] NA
> [1] NA
> [1] NA
>
>> for(i in 1:10) print(f[[i]](1))
> [1] 1.2
> [1] 1.45
> [1] 1.38
> [1] 1.9
> [1] NA
> [1] NA
> [1] NA
> [1] NA
> [1] NA
> [1] NA
>
> HTH,
> Dennis
>
> On Mon, Feb 14, 2011 at 9:50 PM, Eduardo de Oliveira Horta
> <eduardo.oliveirahorta at gmail.com> wrote:
>>
>> Hello again.
>>
>> Let me try something a little more intricate. Let's say instead of
>> forcing evaluation of 'i' I'd want to force evaluation of a vector;
>> for example:
>> s <- c( 0.2, 0.45, 0.38, 0.9)
>> f  <- lapply(1:10, function(i)local({ force(i) ; function(x)x^2+s[i]}))
>> rm(s)
>> f[[1]](0.1)
>> Error in f[[1]](0.1) : object 's' not found
>>
>> Any thoughts?
>>
>> Best regards,
>>
>> Eduardo
>>
>> > sessionInfo()
>> R version 2.11.1 (2010-05-31)
>> x86_64-pc-mingw32
>>
>> locale:
>> [1] LC_COLLATE=Portuguese_Brazil.1252  LC_CTYPE=Portuguese_Brazil.1252
>> [3] LC_MONETARY=Portuguese_Brazil.1252 LC_NUMERIC=C
>> [5] LC_TIME=Portuguese_Brazil.1252
>>
>> attached base packages:
>> [1] stats     graphics  grDevices utils     datasets  methods   base
>>
>> other attached packages:
>> [1] Revobase_4.2.0   RevoScaleR_1.1-1 lattice_0.19-13
>>
>> loaded via a namespace (and not attached):
>> [1] grid_2.11.1       pkgXMLBuilder_1.0 revoIpe_1.0       tools_2.11.1
>> [5] XML_3.1-0
>>
>> > On Mon, Nov 15, 2010 at 7:10 PM, William Dunlap <wdunlap at tibco.com>
>> > wrote:
>> >> You could make f[[i]] be function(t)t^2+i for i in 1:10
>> >> with
>> >>     f <- lapply(1:10, function(i)local({ force(i) ; function(x)x^2+i}))
>> >> After that we get the correct results
>> >>    > f[[7]](100:103)
>> >>    [1] 10007 10208 10411 10616
>> >> but looking at the function doesn't immdiately tell you
>> >> what 'i' is in the function
>> >>    > f[[7]]
>> >>    function (x)
>> >>    x^2 + i
>> >>    <environment: 0x19d7458>
>> >> You can find it in f[[7]]'s environment
>> >>    > get("i", envir=environment(f[[7]]))
>> >>    [1] 7
>> >>
>> >> The call to force() in the call to local() is not
>> >> necessary in this case, although it can help in
>> >> other situations.
>> >>
>> >> 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 Eduardo de
>> >>> Oliveira Horta
>> >>> Sent: Monday, November 15, 2010 12:50 PM
>> >>> To: r-help at r-project.org
>> >>> Subject: [R] Defining functions inside loops
>> >>>
>> >>> Hello,
>> >>>
>> >>> I was trying to define a set of functions inside a loop, with
>> >>> the loop index
>> >>> working as a parameter for each function. Below I post a
>> >>> simpler example, as
>> >>> to illustrate what I was intending:
>> >>>
>> >>> f<-list()
>> >>> for (i in 1:10){
>> >>>   f[[i]]<-function(t){
>> >>>     f[[i]]<-t^2+i
>> >>>   }
>> >>> }
>> >>> rm(i)
>> >>>
>> >>> With that, I was expecting that f[[1]] would be a function
>> >>> defined by t^2+1,
>> >>> f[[2]] by t^2+2 and so on. However, the index i somehow
>> >>> doesn't "get in" the
>> >>> function definition on each loop, that is, the functions
>> >>> f[[1]] through
>> >>> f[[10]] are all defined by t^2+i. Thus, if I remove the
>> >>> object i from the
>> >>> workspace, I get an error when evaluating these functions.
>> >>> Otherwise, if
>> >>> don't remove the object i, it ends the loop with value equal
>> >>> to 10 and then
>> >>> f[[1]](t)=f[[2]](t)=...=f[[10]](t)=t^2+10.
>> >>>
>> >>> I am aware that I could simply put
>> >>>
>> >>> f<-function(u,i){
>> >>>   f<-t^2+i
>> >>> }
>> >>>
>> >>> but that's really not what I want.
>> >>>
>> >>> Any help would be appreciated. Thanks in advance,
>> >>>
>> >>> Eduardo Horta
>> >>>
>> >>>       [[alternative HTML version deleted]]
>> >>>
>> >>> ______________________________________________
>> >>> 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.
>
>