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<?php $arr=[ [ 'date' => '2019-12-29', 'event' => 'name1' ], [ 'date' => '2019-12-31', 'event' => 'name2' ], [ 'date' => '2019-12-29', 'event' => 'name3' ], [ 'date' => '2019-12-30', 'event' => 'name4' ], [ 'date' => '2019-12-29', 'event' => 'name5' ], [ 'date' => '2019-12-31', 'event' => 'name6' ], [ 'date' => '2019-12-29', 'event' => 'name7' ], [ 'date' => '2019-12-30', 'event' => 'name8' ], [ 'date' => '2019-12-30', 'event' => 'name9' ], ]; foreach ($arr as $value) { $date[($value['date'])][]=$value['event']; } ksort($date); print_r($date);