Dear R-users,
I'm struggling in R in order to "squeeze" a matrix without using a
for-loop.
Although my case is a bit more complex, the following example should
help you to understand what I would like to do, but without the slow
for-loop.
Thanks in advance,
Carlo Giovanni Camarda


A  <- matrix(1:54, ncol=6)      # my original matrix
A.new <- matrix(nrow=3, ncol=6) # a new matrix which I'll fill
# for-loop
for(i in 1:nrow(A.new)){
    B <- A[i:(i+2), ]   # selecting the rows
    C <- apply(B,2,sum) # summing by columns
    A.new[i,] <- C      # inserting in the new matrix
}


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