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

Marc Mamin M.Mamin at intershop.de
Tue Jun 8 15:38:10 CEST 2004


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



V1	V2	V3
a	x	6
a	y	8
b	z	16

Thanks for your hints .


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