[R] vectorizaton

From: Dimitri Joe <dimitrijoe_at_yahoo.com.br>
Date: Wed 13 Jul 2005 - 00:24:00 EST


I got 1000 NxN matrices grouped in one array. I want one matrix in which p_ij is the average of all the 1000 matrices in the array. Here's what I'm trying to do:

# P is the NxNx1000 array

for(i in 1:N)
for(j in 1:N)
for(k in 1: 1000)

mymat[ i, j ] <- mean( P [i , j , k ] )

Otherwise, I could have a NxNx1000 vector, and get the N^2 means of the 1+ (N^2)*(0: 999) elements. I don't know which is more efficient, but I wouldn't know how to carry this last solution out anyway. Any ideas on how to do this efficiently?



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