For the general case of an n x m matrix:
(note n & m evenly divisible by i & j respectively) 
$rows = n;
$cols = m;
$rowstep = i;
$colstep = j;
$num_row_subs = $rows/$rowstep;
$num_col_subs = $cols/$colstep;

for $r (0 .. $num_row_subs-1) {
    for $c (0 .. $num_col_subs-1) {
        for $sub_row (0 .. $rowstep-1) {
            for $sub_col (0 .. $colstep-1) {
                $row = $r*$rowstep+$sub_row;
                $col = $c*$colstep+$sub_col;
                print "[$r*$rowstep+$sub_row = $row][$c*$colstep+$sub_
+col = $col]<br>\n";
            }
        }
    }
}

[download]
Switching order of for-loops changes manner of walking through sub-matrices.

In reply to Re: Iterating over Blocks of 2-Dim Array by punchcard_don
in thread Iterating over Blocks of 2-Dim Array by Kozz

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