Dear jonathanbriggs,
Try

x <- read.table(textConnection("CustID itemID
1        a
1        b
2        c
3        a
3        c"),header=TRUE)
closeAllConnections()

with(x, tapply(CustID, itemID, paste, collapse=",") )
#   a    b    c
# "1,3"  "1" "2,3"

with(x, tapply(itemID, CustID, paste, collapse=",") )
#   1    2    3
#"a,b"  "c" "a,c"

HTH,

Jorge


On Sun, Jun 7, 2009 at 1:26 PM, jonathanbriggs <jonathanbriggs@mac.com>wrote:

>
> Apologies if this is an obvious question but I am teaching myself R and the
> occasional push in the right direction is much appreciated?
>
> I have a data.frame containing data that looks like this
>
> CustID itemID
> 1        a
> 1        b
> 2        c
> 3        a
> 3        c
>
> I want to assemble the vector of all the items bought by a particular
> customer and can't quite see how to do it.
>
> What is the best way to represent the answers for a single customer and by
> all customers?
>
> Thanks.
> --
> View this message in context:
> http://www.nabble.com/How-do-I-construct-a-one-matrix-from-another--%28newbie%29-tp23913248p23913248.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help@r-project.org mailing list
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> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

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