[R] Newbie: Ranking a data frame, grouped by 2 or more columns
hadley wickham
h.wickham at gmail.com
Fri Sep 26 23:54:10 CEST 2008
On Fri, Sep 26, 2008 at 3:54 PM, Matthew Pettis
<matthew.pettis at gmail.com> wrote:
> Hi,
>
> I'd like to rank obs in a data frame as subset by 2 or more columns...
> The example input would look like the following:
>
> ====+====+====+====+
> x y v
> -- -- --
> a w 200
> a w 100
> b w 500
> b w 200
> b z 300
> b z 400
> ====+====+====+====+
>
> And the data frame I want to create is below:
> ====+====+====+====+
> x y v rank
> -- -- -- ----
> a w 200 1
> a w 100 2
> b w 500 1
> b w 200 2
> b z 300 2
> b z 400 1
> ====+====+====+====+
>
> Can someone help me with this?
This is easy to do with the (very soon to be released) plyr package:
library(plyr)
ddply(df, .(x, y), transform, rank = rank(v))
You can learn more about it at http://had.co.nz/plyr
Hadley
--
http://had.co.nz/
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