<?php
/**
 * @link http://stackoverflow.com/q/9445369/367456
 */
 
$array = range('A', 'M');
$columns = 4;
$length = count($array);
 
print_matrix($array, $columns);
 
$floor = floor($length/$columns);
$modulo = $length % $columns;
$max = $length-1;
$virtual = 0;
$keys = array_keys($array);
$build = array();
foreach($keys as $index => $key)
{
    $vkey = $keys[$virtual];
    $build[$vkey] = $array[$vkey];
    $virtual += $floor + ($index % $columns < $modulo);
    ($virtual>$max) && $virtual %= $max;
}
 
print_matrix($build, $columns);
 
function print_matrix($matrix, $columns)
{
    echo "One row - " . implode(' ', $matrix) . "\n";
 
    foreach(array_chunk($matrix, $columns, 1) as $row)
    {
        foreach($row as $key => $col)
            printf('%s[%2d] ', $col, $key);
        echo "\n";
    }
    echo "\n";
}

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