ridiculous date string comparison

stupid_logic.php

<?php

// Make sales chart data
$i = 1;
foreach ($master['eom'] as $key => $eom) {
    $key_compare = intval(substr($key, -2));
    $starting_index_month = intval(substr($EOM_STARTING_INDEX + ($i - 1), -2));
    $month_compare = $starting_index_month <= 12 ? $starting_index_month : $starting_index_month - 12;

    $diff = $key_compare - $month_compare;
    $i = $i + $diff;
    $m = date('M y', strtotime($eom->datetime));
    $labels[$i] = $m;

    // Append to data arrays
    $data_sold[$i] = intval($eom->sold_units);
    $data_returned[$i] = intval(abs($eom->returned_units));
    $data_netunits[$i] = $data_sold[$i] - $data_returned[$i];

    $i++;
}

?>