[R] by-group processing

[hadley wickham]

On Wed, May 6, 2009 at 8:12 PM, jim holtman <jholtman at gmail.com> wrote:
> Ths should do it:
>
>> do.call(rbind, lapply(split(x, x$ID), tail, 1))
>         ID Type N
> 45900 45900    I 7
> 46550 46550    I 7
> 49270 49270    E 3


Or with plyr:

library(plyr)
ddply(x, "id", tail, 1)

plyr encapsulates the common split-apply-combine strategy and takes
cares of the details for you.  Read more about it on
http://had.co.nz/plyr

Hadley


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