[R] Wrap a loop inside a function

[Doran, Harold]

Very true, the resounding echo was large.

Thanks, Doug. 

> -----Original Message-----
> From: dmbates at gmail.com [mailto:dmbates at gmail.com] On Behalf 
> Of Douglas Bates
> Sent: Wednesday, July 19, 2006 4:20 PM
> To: Doran, Harold
> Cc: r-help at stat.math.ethz.ch
> Subject: Re: [R] Wrap a loop inside a function
> 
> I'm sure when you read this there will be the sound of a palm 
> slapping a forehead.  :-)
> 
> The value of a function is the value of the last expression 
> evaluated in the function.  If you rewrite foo as
> 
> 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]])
>   like.mat
>   }
> 
> you will get the result that you want.
> 
> On 7/19/06, Doran, Harold <HDoran at air.org> 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]]
> >
> > ______________________________________________
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> > 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.
> >
>