/**
* @return \Traver\Collection\Builder
*/
protected function createBuilder()
{
return ImmutableMap::newBuilder();
}
/**
* @param callable $keyFunction
* @return PipeableLike
* @see Pipeable::groupBy
*/
public function groupBy(callable $keyFunction)
{
$keyFunction = self::wrapCallback($keyFunction);
$result = [];
foreach ($this->asTraversable() as $key => $value) {
$groupKey = $keyFunction($value, $key);
if (!isset($result[$groupKey])) {
$result[$groupKey] = [];
}
$result[$groupKey][$key] = $value;
}
$builder = ImmutableMap::newBuilder();
foreach ($result as $key => $group) {
$groupPipeable = $this->newCollection($group);
$builder->add($groupPipeable, $key);
}
return $builder->build();
}