[R] Wrap a loop inside a function

From: Doran, Harold <HDoran_at_air.org>
Date: Thu 20 Jul 2006 - 06:09:04 EST


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)

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