removeDuplicates()

<?php
    /**
    * Removes values from an array if they are shown more than once
    *
    * @param array $arr
    * @return array
    */
    function removeDuplicates($arr) {
        if (!is_array($arr)) { // Error handling
            return $arr;
        }

        // Temporary array with every value found
        $tempArr = array();

        foreach ($arr AS $key => $val) {
            if (isset($tempArr[$val])) { // If value is already found...
                // ... unset the first key found and the actual key...
                unset($arr[$tempArr[$val]], $arr[$key]);
            } else { // ... otherwise, mark this value as found
                $tempArr[$val] = $key;
            }
        }

        // Return array with rearranged keys
        return array_values($arr);
    }

    // --------------------
    // Set up test environment
    $size = 100000; // Size of array to remove duplicates from
    $diversity = 10000; // number of different values in test array

    // Fill array with random numeric values
    $array = array();
    for ($i = 0; $i < $size; $i++) {
        $array[] = rand(0,$diversity);
    }

    // --------------------
    // Start test

    $start = microtime(true);

    removeDuplicates($array);

    var_dump(microtime(true) - $start);