Tim’s
Bandwagon

<?php
 
/**
 * Calculates the frequently occuring value(s) in an array.
 *
 * @param  array $data
 * @return array
 */
function array_mode($data)
{
    if(!is_array($data)) {
        throw new Exception('First argument $data must be an array.');
    }
    $frequencies = array_count_values($data);
    // Double-check that frequencies are sorted in reverse order,
    // I think array_count_values actually returns in this format
    // already, but the manual doesn't mention it.
    arsort($frequencies);
    $isFirst = true; // Yuk
    $mode = array();
    foreach ($frequencies as $thisValue=>$thisFrequency) {
        if ($isFirst == true) {
            $isFirst = false; // Wince
            $mode[] = $thisValue;
            $modeFrequency = $thisFrequency;
            continue;
        }
        if ($modeFrequency == $thisFrequency) {
            $mode[] = $thisValue;
        }
        if ($modeFrequency > $thisFrequency) {
            break;
        }
    }
    return $mode;
}
 
var_dump(array_mode(array('a', 'a', 'b', 'c', 'd')));
/*
array(1) {
  [0]=>
  string(1) "a"
}
*/
 
var_dump(array_mode(array('a', 'a', 'b', 'b', 'c')));
/*
array(2) {
  [0]=>
  string(1) "a"
  [1]=>
  string(1) "b"
}
*/