[R] Wrap a loop inside a function

[Sundar Dorai-Raj]

Doran, Harold wrote:
> I need to wrap a loop inside a function and am having a small bit of
> difficulty getting the results I need. Below is a replicable example.
> 
> 
> # define functions
> pcm <- function(theta,d,score){
>      exp(rowSums(outer(theta,d[1:score],'-')))/
>      apply(exp(apply(outer(theta,d, '-'), 1, cumsum)), 2, sum)
>    }
> 
> foo <- function(theta,items, score){ 
>    like.mat <- matrix(numeric(length(items) * length(theta)), ncol =
> length(theta))   
>    for(i in 1:length(items)) like.mat[i, ] <- pcm(theta, items[[i]],
> score[[i]]) 
>    }
> 
> # begin example
> theta <- c(-1,-.5,0,.5,1)
> items <- list(item1 = c(0,1,2), item2 = c(0,1), item3 = c(0,1,2,3,4),
> item4 = c(0,1))
> score <- c(2,1,3,1) 
> (foo(theta, items, score))
> 
> # R output from function foo
> [1] 0.8807971 0.8175745 0.7310586 0.6224593 0.5000000
> 
> 
> However, what I am expecting from the function foo is
> 
> 
>>like.mat
> 
>             [,1]       [,2]       [,3]       [,4]      [,5]
> [1,] 0.118499655 0.17973411 0.25949646 0.34820743 0.4223188
> [2,] 0.880797078 0.81757448 0.73105858 0.62245933 0.5000000
> [3,] 0.005899109 0.01474683 0.03505661 0.07718843 0.1520072
> [4,] 0.880797078 0.81757448 0.73105858 0.62245933 0.5000000
> 
> 
> I cannot seem to track down why the function foo is only keeping the
> last row of the full matrix I need. Can anyone see where my error is?
> 
> Thanks,
> Harold
> 
> platform       i386-pc-mingw32           
> arch           i386                      
> os             mingw32                   
> system         i386, mingw32             
> status                                   
> major          2                         
> minor          3.0                       
> year           2006                      
> month          04                        
> day            24                        
> svn rev        37909                     
> language       R                         
> version.string Version 2.3.0 (2006-04-24)
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at stat.math.ethz.ch 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.


Hi, Harold,

Your function "foo" is only returning the last call from "for". Try:

foo <- function(theta,items, score){
   like.mat <- matrix(numeric(length(items) * length(theta)),
                      ncol = length(theta))
   for(i in 1:length(items))
     like.mat[i, ] <- pcm(theta, items[[i]], score[[i]])
   ## return like.mat, not just the last line from "for"
   like.mat
}


HTH,

--sundar