Online PHP editor | refs for qWO1f

<?php class Foo { private $groupId; private $value; function __construct($groupId, $value) { $this->groupId = $groupId; $this->value = $value; } function getGroupId() { return $this->groupId; } }; $foos = [ new Foo(1, 'Bar'), new Foo(1, 'Ban'), new Foo(1, 'Bak'), new Foo(2, 'Gas'), new Foo(2, 'Gar'), ]; var_dump(array_reduce($foos, function($carry, $item){ if(!isset($carry[$item->getGroupId()])) { $carry[$item->getGroupId()] = []; } $carry[$item->getGroupId()][] = $item; return $carry; }, []));