Hello,
Try the following.
sapply(1:(30 - 2), function(i) sum(el[i:(i+2), ]))
but with number of rows instead of 30.
Hope this helps,
Rui Barradas
Em 09-05-2014 22:35, eliza botto escreveu:
Dear useRs,
I have a matrix, say "el" of 30 rows and 10 columns, as
el<-matrix(sample(1:300),ncol=10)
I want to sum up various sets of three rows of each column in the following
manner
sum(el[c(1,2,3),]) ##adding row number 1, 2 and 3 of each column
sum(el[c(2,3,4),])##adding row number 2, 3 and 4 of each column
sum(el[c(3,4,5),])##adding row number 3, 4 and 5 of each column
sum(el[c(4,5,6),])
sum(el[c(5,6,7),])
sum(el[c(6,7,8),])
sum(el[c(7,8,9),])
sum(el[c(8,9,10),])
sum(el[c(9,10,11),])
................
......
so on
..............
I know how to do it manually, but since my original matrix has 2000 rows, I
therefore want to figure out a more conveinient way.
Thankyou so very much in advance,
Eliza
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