Timo Schneider wrote:
>
>
> I have a dataframe (obtained from read.table()) which looks like
>
> ExpA ExpB ExpC Size
> 1 12 23 33 1
> 2 12 24 29 1
> 3 10 22 34 1
> 4 25 50 60 2
> 5 24 53 62 2
> 6 21 49 61 2
>
> now I want to take all rows that have the same value in the "Size"
> column and apply a function to the columns of these rows (for example
> median()). The result should be a new dataframe with the medians of the
> groups, like this:
>
>
Besides the mentioned aggregate, you could use one of the functions in
package plyr.
Dieter
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