If one element in the PHP array is the same, how to splice other elements-php Tutorial

If one element in the PHP array is the same, how can we splice other elements, such as the original array?
Array (3 ){
[0] => array (6 ){
["Pla_id"] => string (3) "298"
["User_id"] => string (1) "1"
["Due_in"] => string (15) "8.33"
}
[1] => array (6 ){
["Pla_id"] => string (3) "976"
["User_id"] => string (1) "1"
["Due_in"] => string (15) "338.90"
}
[2] => array (6 ){
["Pla_id"] => string (3) "56"
["User_id"] => string (1) "2"
["Due_in"] => string (15) "25.6"
}}
Because the user_id = 1 in the array is the same
To get the final array like this, how do I write (that is, concatenate other elements with the same user_id )?
Array (3 ){
[0] => array (6 ){
["Pla_id"] => string (3) "298,976"
["User_id"] => string (1) "1"
["Due_in"] => string (15) "8.33, 338.90"
}
[1] => array (6 ){
["Pla_id"] => string (3) "56"
["User_id"] => string (1) "2"
["Due_in"] => string (15) "25.6"
}}

Reply to discussion (solution)

$a = array(  array(    "pla_id" => "298",    "user_id" => "1",    "due_in" => "8.33",  ),  array(    "pla_id" => "976",    "user_id" => "1",    "due_in" => "338.90",  ),  array(    "pla_id" => "56",    "user_id" => "2",    "due_in" => "25.6",  ));$b = array();foreach($a as $v) {  if(! isset($b[$v['user_id']])) $b[$v['user_id']] = $v;  else $b[$v['user_id']]["due_in"] .= ',' . $v["due_in"];}var_dump(array_values($b));

array(2) {  [0]=>  array(3) {    ["pla_id"]=>    string(3) "298"    ["user_id"]=>    string(1) "1"    ["due_in"]=>    string(11) "8.33,338.90"  }  [1]=>  array(3) {    ["pla_id"]=>    string(2) "56"    ["user_id"]=>    string(1) "2"    ["due_in"]=>    string(4) "25.6"  }}

$a = array(  array(    "pla_id" => "298",    "user_id" => "1",    "due_in" => "8.33",  ),  array(    "pla_id" => "976",    "user_id" => "1",    "due_in" => "338.90",  ),  array(    "pla_id" => "56",    "user_id" => "2",    "due_in" => "25.6",  ));$b = array();foreach($a as $v) {  if(! isset($b[$v['user_id']])) $b[$v['user_id']] = $v;  else $b[$v['user_id']]["due_in"] .= ',' . $v["due_in"];}var_dump(array_values($b));

array(2) {  [0]=>  array(3) {    ["pla_id"]=>    string(3) "298"    ["user_id"]=>    string(1) "1"    ["due_in"]=>    string(11) "8.33,338.90"  }  [1]=>  array(3) {    ["pla_id"]=>    string(2) "56"    ["user_id"]=>    string(1) "2"    ["due_in"]=>    string(4) "25.6"  }}

Thank you. thank you very much.