<?php
  /**
   * It's hard to believe this isn't a PHP builtin.
   *
   * @param $source array to pull a subset of key/value pairs out of
   * @param $keys list of keys to pull out
   * @return $result array
   */
  function array_subset_of_the_array_based_on_a_list_of_keys (array $source, array $keys)
  {
    $result = array();
    foreach ($keys as &$key)
      $result[$key] = $source[$key];
    return $result;
  }

  function faster_version (array $source, array $keys)
  {
    $result = array();
    for ($i = 0, $size = count($keys); $i < $size; ++$i) {
      $key = $keys[$i];
      $result[ $key ] = $source[ $key ];
    }
    return $result;
  }

$keys = array('one', 'two', 'three', 'four', 'five', 'six');

$source = array(
  'one' => 'blakdlajsfdlkajfds;lasjkflaksjf',
  'two' => 'asdfkljasfkjsadfas;jdfas ldfjk',
  'three' => 'alk;sjdfasklfjaslf;ja',
  'four' => '6',
  'five' => 2,
  'six' => 12314
);

$start = microtime(true);

for ($i = 0, $size = 100000; $i < $size; ++$i) {
  $pulled = faster_version($source, array('one', 'three', 'five'));
}

$time1 = microtime(true) - $start;

$start = microtime(true);

for ($i = 0, $size = 100000; $i < $size; ++$i) {
  $pulled = array_subset_of_the_array_based_on_a_list_of_keys($source, array('one', 'three', 'five'));
}

$time2 = microtime(true) - $start;

echo "time1: $time1\ntime2: $time2\n";