[R] Computting statistics on a matrix with 2 factor column

[Chuck Cleland]

?tapply
?aggregate

   You probably have a data frame, not a matrix.

Marc Mamin wrote:
> I suppose this is a basic question but couldn't find a solution.:
> 
> I have a large matrix with let say 3 columns:
> 
> V1	V2	V3
> a	x	2
> a	x	4
> a	y	8
> b	z	16
> 
> and I want to compute some statistics based on 
> the levels resulting form the combination of the two first columns
> 
> e.g.:
> 
> SUM->
> 
> V1	V2	V3
> a	x	6
> a	y	8
> b	z	16

-- 
Chuck Cleland, Ph.D.
NDRI, Inc.
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