http://stackoverflow.com/questions/173400/php-arrays-a-good-way-to-check-if-an-array-is-associative-or-sequential

gistfile1.txt

<?php

function isAssoc($arr)
{
    return array_keys($arr) !== range(0, count($arr) - 1);
}

function is_assoc($array) {
    return (bool)count(array_filter(array_keys($array), 'is_string'));
}

function isSequential($arr)
{
    return array_values($arr) === $arr;
}

function is_indexed_array($arr) {
    for (reset($arr); is_int(key($arr)); next($arr));
    return is_null(key($arr));
}

function is_sequential_array($arr, $base = 0) {
    for (reset($arr), $base = (int) $base; key($arr) === $base++; next($arr));
    return is_null(key($arr));
}

$fatArray = array();
for ($i = 0; $i < 999999; $i++) {
    $fatArray[$i] = rand();
}
#$fatArray['test'] = 1;
echo $before = memory_get_peak_usage() . "\n";
echo $timeBefore = microtime(true);
var_dump(isSequential($fatArray));
echo $timeAfter = microtime(true);
echo $after = memory_get_peak_usage() . "\n";

echo ($timeAfter-$timeBefore) . " s\n";
echo ($after-$before)/1024/1024 . " MB\n";