[PHP] 轉換資料：for-loop vs. array_map()

/**
 * Origin:
 *  array(
 *    array('id' => 'x'),
 *    array('id' => 'y'),
 *    array('id' => 'z'),
 *  );
 * Expect:
 *  array('x', 'y', 'z');
 */
function calc($t0, $t1)
{
   $v0 = array_sum(explode(' ', $t0));
   $v1 = array_sum(explode(' ', $t1));
   $sub = $v1 - $v0;
   echo "$v1 - $v0 = $sub\n";
   return $sub;
}

$origin = array(array('id' => 'x'), array('id' => 'y'), array('id' => 'z'));

$t0 = microtime();
for ($i = 0; $i < 1E6; $i++) {
   $expect = array();
   foreach ($origin as $o) {
      $expect[] = $o['id'];
   }
}
$t1 = microtime();
$method1 = calc($t0, $t1);     // output: 1420770195.046 - 1420770193.6821 = 1.3638761043549

$t0 = microtime();
for ($i = 0; $i < 1E6; $i++) {
   $expect = array_map(function ($o) { return $o['id']; }, $origin);
}
$t1 = microtime();
$method2 = calc($t0, $t1);     // output: 1420770202.2368 - 1420770195.0461 = 7.1907830238342

echo ($method2 - $method1) / $method2; // output: 0.81032995991755

從測試中可以知道 array_map() 比 for-loop 慢。不過 array_map() 寫法比較簡潔。

補充，引用外部參數：

   $key = 'id';
   $expect = array_map(function ($o) use ($key) { return $o[$key]; }, $origin);

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