array_column implementation for PHP <= 5.5

function array_column(array $input, $columnKey, $indexKey = null)
{
 $array = array();
 foreach ($input as $value) {
 if ( ! isset($value[$columnKey])) {
 trigger_error("Key \"$columnKey\" does not exist in array");
 return false;
 }

 if (is_null($indexKey)) {
 $array[] = $value[$columnKey];
 } else {
 if ( ! isset($value[$indexKey])) {
 trigger_error("Key \"$indexKey\" does not exist in array");
 return false;
 }
 if ( ! is_scalar($value[$indexKey])) {
 trigger_error("Key \"$indexKey\" does not contain scalar value");
 return false;
 }
 $array[$value[$indexKey]] = $value[$columnKey];
 }
 }

 return $array;
}

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