How to stitch other elements in a PHP array if one element is the same

For example, the original array is like this
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 last such array, how do you write (that is, user_id the same other elements together)?
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 (    "pla_id" = "298",    "user_id" and "1",    "due_in" and "8.33",  ),  Array (    "pla_id" = "976",    "user_id" and "1", "due_in" and "338.90", ",",  Array (    "pla_id" = > "user_id",    "2", "    due_in" and "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 (one) "8.33,338.90"  }  [1]=>  Array (3) {    ["Pla_ ID "]=>    string (2)"    ["user_id"]=>    string (1) "2"    ["due_in"]=>    string (4) "25.6"  }}

$a = Array (    "pla_id" = "298",    "user_id" and "1",    "due_in" and "8.33",  ),  Array (    "pla_id" = "976",    "user_id" and "1", "due_in" and "338.90", ",",  Array (    "pla_id" = > "user_id",    "2", "    due_in" and "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 (one) "8.33,338.90"  }  [1]=>  Array (3) {    ["Pla_ ID "]=>    string (2)"    ["user_id"]=>    string (1) "2"    ["due_in"]=>    string (4) "25.6"  }}

Thanks, thank you so much.

