Syntax: toLookup ([keySelector {(v, k) ==> key} [, valueSelector {(v, k) ==> value}]])
The toLookup method returns an array, a one-to-many dictionary that maps keys to arrays of values.
| public toLookup ( callable | null $keySelector = null, callable | null $valueSelector = null ) : array | ||
| $keySelector | callable | null | {(v, k) ==> key} A function to extract a key from each element. Default: key. |
| $valueSelector | callable | null | {(v, k) ==> value} A transform function to produce a result value from each element. Default: value. |
| return | array | An array that contains keys and value arrays selected from the input sequence. |
public function toLookup($keySelector = null, $valueSelector = null)
{
$keySelector = Utils::createLambda($keySelector, 'v,k', Functions::$key);
$valueSelector = Utils::createLambda($valueSelector, 'v,k', Functions::$value);
$lookup = [];
foreach ($this as $k => $v) {
$lookup[$keySelector($v, $k)][] = $valueSelector($v, $k);
}
return $lookup;
}