Collapse data matrix with extra info separated by commas

test <-

data.frame(a=c("A","A","A","A","B","B","B"),b=c(1,1,2,2,1,1,1),c=1:7)

Hello,

I would like to reshape my data for presentation purposes from  
something
like this:

test <-

data.frame(a=c("A","A","A","A","B","B","B"),b=c(1,1,2,2,1,1,1),c=1:7)

test

 a b c
1 A 1 1
2 A 1 2
3 A 2 3
4 A 2 4
5 B 1 5
6 B 1 6
7 B 1 7

to something like this:
 a b c
1 A 1 1,2
3 A 2 3,4
5 B 1 5,6,7

This seems to be the sort of the thing that the reshape library should
be able to do, but I just can't work out how to do it.

Many thanks

Dan

-- 
**************************************************************
Daniel Brewer, Ph.D.

Institute of Cancer Research
Molecular Carcinogenesis
Email: daniel.brewer at icr.ac.uk
**************************************************************

The Institute of Cancer Research: Royal Cancer Hospital, a  
charitable Company Limited by Guarantee, Registered in England under  
Company No. 534147 with its Registered Office at 123 Old Brompton  
Road, London SW7 3RP.

This e-mail message is confidential and for use by the...{{dropped:26}}

x <- lapply(split(test, list(test$a, test$b), drop=TRUE), function(.data){

do.call(rbind, x)

Hello,

I would like to reshape my data for presentation purposes from something
like this:

test <-

data.frame(a=c("A","A","A","A","B","B","B"),b=c(1,1,2,2,1,1,1),c=1:7)

test

?a b c
1 A 1 1
2 A 1 2
3 A 2 3
4 A 2 4
5 B 1 5
6 B 1 6
7 B 1 7

to something like this:
?a b c
1 A 1 1,2
3 A 2 3,4
5 B 1 5,6,7

This seems to be the sort of the thing that the reshape library should
be able to do, but I just can't work out how to do it.

Many thanks

Dan

--
**************************************************************
Daniel Brewer, Ph.D.

Institute of Cancer Research
Molecular Carcinogenesis
Email: daniel.brewer at icr.ac.uk
**************************************************************

The Institute of Cancer Research: Royal Cancer Hospital, a charitable Company Limited by Guarantee, Registered in England under Company No. 534147 with its Registered Office at 123 Old Brompton Road, London SW7 3RP.

This e-mail message is confidential and for use by the...{{dropped:19}}

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])