Function to zipper two arrays together. Preserves keys, appending unique value if duplicated.

gistfile1.php

<?php

/**
 * zippers two arrays together, alternating values from each array
 * 
 * @param array $array1
 * @param array $array2
 * @return array
 */
function zipperArrays(array $array1, array $array2) {
    $zippered = array();

    /*    
     * recursive function returning a key value unique across all arrays involved.
     * appends number-based identifier (_1, _2, etc) to array key if it already exists.
     * does not overwrite underscore values that already exist in the arrays to be zippered
     */ 
    $getUniqueKey = function($needle, $level = 0) use(&$getUniqueKey, &$zippered, $array1, $array2) {
        $uniqueNeedle = $level ? $needle.'_'.$level : $needle;

        $append = '_' . $level;            
        if (array_key_exists($uniqueNeedle, $zippered) 
                || (substr_compare($uniqueNeedle, $append, -strlen($append), strlen($append)) === 0 
                        && (array_key_exists($uniqueNeedle, $array1) || array_key_exists($uniqueNeedle, $array2)))) {
            return $getUniqueKey($needle, ++$level);
        }
        return $uniqueNeedle;
    };

    /*
     * takes an array from each() and adds the value (and key, if a string-based key is given) to $zippered.
     * does not preserve numeric indexes
     */
    $addValue = function(array $item) use(&$getUniqueKey, &$zippered) {
        if (is_numeric($item['key'])) {
            $zippered[] = $item['value'];
        } else {
            $zippered[$getUniqueKey($item['key'])] = $item['value'];
        }
    };

    while ($item = each($array1)) {
        $addValue($item);

        $item2 = each($array2);
        if ($item2) {
            $addValue($item2);
        }
    }

    // ensures that if $array2 is longer than $array1, the remainder of its values will be added to $zippered
    while ($item = each($array2)) {
        $addValue($item);
    }

    return $zippered;
}

?>