On 02/10/11 14:06, Jim Silverton wrote:
Hi all,
I have 2 columns in a mtrix, one of which is a column of probabilities and
the other is simply a vector of integers. I want to sum all the
probabilities with the same integer value and put it in a new column.
For example,
If my matrix is:
0.98 2
0.2 1
0.01 2
0.5 1
0.6 6
Then I should get:
0.98 2 0.99
0.2 1 0.70
0.01 2 0.99
0.5 1 0.70
0.6 6 0.60
Any help is greatly appreciated.
Suppose your matrix is called "m". Execute:
> ttt <- tapply(m[,1],m[,2],sum)
> m <- cbind(m,ttt[match(m[,2],names(ttt))])
> dimnames(m) <- NULL # To tidy up a bit.
You get:
> m
[,1] [,2] [,3]
[1,] 0.98 2 0.99
[2,] 0.20 1 0.70
[3,] 0.01 2 0.99
[4,] 0.50 1 0.70
[5,] 0.60 6 0.60
Easy-peasy.
cheers,
Rolf Turner
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