see ?aggregate
m<-rbind(sample(2:6,9,replace=T),sample(1:3,9,replace=T))
aggregate(m[2,],by=list(m[1,]),sum)
Hans-Henning Gabriel schrieb:
Hi,
my problem is as follows:
I have a matrix of two rows like this:
2 2 3 4 4 4 5 5 6
1 1 2 1 3 3 2 1 1
Can I apply something like "group by" in sql? What I want to achieve
is the some of second row for each unique entry of first row:
2 -> 2 (=1+1)
3 -> 2
4 -> 7 (=1+3+3)
5 -> 3 (=2+1)
6 -> 1
Thanks!!
Henning
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