Dear Splus Users,
When handling a big data set ( 200K * 26 ), I come
across this problem. The data set ( M1 )looks like
this:
> M1
V1 V2 V3
1 A X 4
2 B X 1
3 A Y 2
4 A X 3
5 B Y 5
6 B Z 6
7 C Z 3
What I want is M2
> M2
V1 V2 V3
1 A X 7
2 B Y 6
3 A Y 2
4 B Z 6
5 C Z 3
that is, I need to add up the V3's for rows with the
same V1 and V2, for example, row 1 and 4, row 2 and 5
in M1.
Could anyone tell me how to do it efficiently?
Thank you.
Haibo
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