Here's a simple and efficient way
A <- matrix(1:12,6,2)
nbin <- 2
dim(A) <- c(nbin, nrow(A)/nbin, 2)
B <- colSums(A)
dim(B) <- dim(A)[-1]
B
[,1] [,2]
[1,] 3 15
[2,] 7 19
[3,] 11 23
On Fri, 14 Jan 2005, Stephen Nyangoma wrote:
I have a large data matrix (4460X3500) and I want to sum row subsets in
groups of 10 (bin). Is there an efficient way to do this in R without
using loops. Looping takes forever to perform this task!
For example suppose we have the matrix
matrix(1:12,6,2)
[,1] [,2]
[1,] 1 7
[2,] 2 8
[3,] 3 9
[4,] 4 10
[5,] 5 11
[6,] 6 12
my problem is to sdum for example:
1. the first and second row
2. the third and fourth
and
3. the fifth and the sixth.
To obtain
[,1] [,2]
[1,] 3 15
[2,] 7 19
[3,] 11 23
--
Brian D. Ripley, [EMAIL PROTECTED]
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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