Online PHP editor | output for odtie

<?php $data = [['id' => 972, 'grouped_by' => 1], ['id' => 664, 'grouped_by' => 4], ['id' => 631, 'grouped_by' => 4], ['id' => 630, 'grouped_by' => 1], ['id' => 971, 'grouped_by' => 1], ['id' => 973, 'grouped_by' => 1], ['id' => 974, 'grouped_by' => 1]]; $grouped_result = $grouped_by_counts = []; $previous_grouped_by = null; // a value that will never occur in the data foreach($data as $datum) { if($datum['grouped_by'] !== $previous_grouped_by) { $grouped_by_counts[$datum['grouped_by']] = isset($grouped_by_counts[$datum['grouped_by']]) ? $grouped_by_counts[$datum['grouped_by']] + 1 : 1; } $grouped_result[ $datum['grouped_by'].'.'.$grouped_by_counts[$datum['grouped_by']] ][] = $datum; $previous_grouped_by = $datum['grouped_by']; } print_r($grouped_result);