[R] Max within groups
dwinsemius at comcast.net
Sat Jul 16 16:16:23 CEST 2011
On Jul 16, 2011, at 9:55 AM, Thomas Chesney wrote:
> I know there's a really easy way to do this but I just can't track
> it down. I experimented with various apply functions but couldn't
> get it quite right.
> I have a matrix like this:
> 1, 16
> 1, 23
> 1, 21
> 1, 6
> 1, 25
> 2, 4
> 2, 17
> 2, 45
> 2, 11
> 2, 20
tapply(mtx[,2], mtx[,1], max)
> and I'd like to find the max value in Column 2 (or the index to the
> max value) grouped by the first column. So the max for Group 1, the
> max for Group 2 etc.
> Any help would be appreciated.
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David Winsemius, MD
West Hartford, CT
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