/**
* Calls a transformation function for each element of an array.
* The function will receive one argument for each specified column.
* It should return an array/object that will replace the original array element.
* Unlike array_map, the original keys will be preserved.
*
* @param array $data
* @param array $cols
* @param callable $fn
*
* @return array A transformed copy of the input array.
*/
function array_mapColumns(array $data, array $cols, callable $fn)
{
$o = [];
foreach ($data as $k => $r) {
$o[$k] = call_user_func_array($fn, array_fields($r, $cols));
}
return $o;
}
/**
* Extracts the values with the given keys from a given array, in the same order as the key list.
*
* @param array $keys A list of keys to be extracted.
* @param mixed $def An optional default value to be returned for non-existing keys.
* @return PowerArray Self, for chaining.
* @see PowerArray::extract
*/
function fields(array $keys, $def = null)
{
$this->A = array_fields($this->A, $keys, $def);
return $this;
}