one way is the following:
M <- cbind(c(1,1,1,1,2,2,3,3,3,3), c(2,2,2,3,4,4,4,5,5,6),
c(1,2,3,4,5,6,7,8,9,10))
ind <- do.call(paste, c(as.data.frame(M[, 1:2], sep = "\r")))
M[, 3] <- ave(M[, 3], ind, FUN = "sum")
unique(M)
I hope it helps.
Best,
Dimitris
On 9/6/2010 4:29 PM, Kennedy wrote:
Hi,
I have a matrix that looks like this
a<- c(1,1,1,1,2,2,3,3,3,3)
b<- c(2,2,2,3,4,4,4,5,5,6)
c<- c(1,2,3,4,5,6,7,8,9,10)
M<- matrix(nr=10,nc=3)
M[,1]<- a
M[,2]<- b
M[,3]<- c
M
[,1] [,2] [,3]
[1,] 1 2 1
[2,] 1 2 2
[3,] 1 2 3
[4,] 1 3 4
[5,] 2 4 5
[6,] 2 4 6
[7,] 3 4 7
[8,] 3 5 8
[9,] 3 5 9
[10,] 3 6 10
I want to reduce the matrix according to the following: If the values of the
two first columns are the same in two or more rows the values in the third
column of the corresponding rows should be added and only one of the rows
should be keept. Hence the matrix M above should look like this
1 2 6
1 3 4
2 4 11
3 4 7
3 5 17
3 6 10
Thank you
Henrik
--
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center
Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
Tel: +31/(0)10/7043478
Fax: +31/(0)10/7043014
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