[R] Help with applying a function to all possible 2x2 submatrices

CMB123 craig.bielski at gmail.com
Mon Oct 22 19:10:26 CEST 2012

Hi all,

I'm working with a large data set (on the order of 300X300) and trying to
apply a function which compares the elements of all possible 2x2
submatrices. There are rc(r-1)(c-1) such submatrices, so obviously the naive
method of looping through the rows and columns is computationally unfeasible
for my data set:

  for(i in 1:(nrow(data)-1)) {
    for(j in (i+1):nrow(data)) {
      for (m in 1:(ncol(data)-1)) {
        for (n in (m+1):ncol(data)) {

I have tried using the outer and apply functions to vectorize the task, but
I can't seem to figure out the best method (or any method, for that matter)
to help with what I'm trying to do. 

Any and all help is much appreciated! Thanks in advance,


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