Online PHP editor | output for 1Bq8e

<?php $array = array ( 0 => array ( 'r_id' => 11, 'r_sid' => 'RC', 'd_id' => 2 ), 1 => array ( 'r_id' => 7, 'r_sid' => 'RC', 'c_id' => 51 ), 2 => array ( 'r_id' => 6, 'r_sid' => 'JN', 'c_id' => 52 ), 3 => array ( 'r_id' => 7, 'r_sid' => 'JN', 'c_id' => 51 ), 4 => array ( 'r_id' => 7, 'r_sid' => 'LG', 'c_id' => 51 ), 5 => array ( 'r_id' => 7, 'r_sid' => 'BN', 'c_id' => 51 ), 6 => array ( 'r_id' => 6, 'r_sid' => 'IVS', 'c_id' => 52 ), 7 => array ( 'r_id' => 7, 'r_sid' => 'IVS', 'c_id' => 51 ) ); // filter out r_sid values which only occur once $sid_values = array_count_values(array_column($array, 'r_sid')); $array = array_filter($array, function ($a) use ($sid_values) { return $sid_values[$a['r_sid']] > 1; }); // combine arrays on r_sid values $result = array(); foreach ($array as $arr) { $sid = $arr['r_sid']; // push data to arrays $result[$sid]['r_sid'] = $sid; $result[$sid]['r_id'][] = $arr['r_id']; if (isset($arr['c_id'])) $result[$sid]['c_id'][] = $arr['c_id']; if (isset($arr['d_id'])) $result[$sid]['d_id'][] = $arr['d_id']; } // combine all the c_id values into a string array_walk($result, function (&$a) { if (isset($a['c_id'])) $a['c_id'] = implode(',', $a['c_id']); }); // now combine any r_sid values that have the same set of c_id values $output = array(); foreach ($result as $res) { $cid = $res['c_id']; // push data to arrays $output[$cid]['c_id'] = $cid; $output[$cid]['r_sid'] = array_merge($output[$cid]['r_sid'] ?? array(), array($res['r_sid'])); $output[$cid]['r_id'] = array_merge($output[$cid]['r_id'] ?? array(), $res['r_id']); if (isset($res['d_id'])) $output[$cid]['d_id'] = array_merge($output[$cid]['d_id'] ?? array(), $res['d_id']); } // combine the r_sid, r_id and d_id values into a string array_walk($output, function (&$a) { $a['r_sid'] = implode(',', $a['r_sid']); $a['r_id'] = implode(',', array_unique($a['r_id'])); if (isset($a['d_id'])) $a['d_id'] = implode(',', $a['d_id']); }); // remove the associative keys $output = array_values($output); print_r($output);