[R] Collapse data matrix with extra info separated by commas

[hadley wickham]

On Mon, Apr 6, 2009 at 10:40 AM, baptiste auguie <ba208 at exeter.ac.uk> wrote:
> Here's one attempt with plyr, hopefully Hadley will give you a better
> solution ( I could not get cast() to do it either)
>
> test <-
> data.frame(a=c("A","A","A","A","B","B","B"),b=c(1,1,2,2,1,1,1),c=sample(1:7))
> ddply(test,.(a,b),.fun=function(.) paste(.)[3])

This is a problem that currently isn't very easy to solve in plyr (but
I'm working on it).  About the best you can do is:

ddply(test, ~ a + b, colwise(paste, .(c)), collapse =",")

(this is basically equivalent to your suggestion)

Hadley


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