[R] Defining functions inside loops

[Eduardo de Oliveira Horta]

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]]
>>>
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>>>
>>
>