php switch array key with subelement key - php

Question

I would like to switch the main keys(0,1,2) of an array with a subelement key(user_id).
For example, from this array:
array(3) {
[0]=>
array(3) {
["num_products_user_by_ref"]=>
string(1) "1"
["user_id"]=>
string(2) "77"
["reference"]=>
string(3) "E49"
}
[1]=>
array(3) {
["num_products_user_by_ref"]=>
string(1) "9"
["user_id"]=>
string(3) "526"
["reference"]=>
string(3) "E49"
}
[2]=>
array(3) {
["num_products_user_by_ref"]=>
string(2) "38"
["user_id"]=>
string(3) "346"
["reference"]=>
string(3) "E49"
}
}
I need :
array(952) {
[77]=>
array(2) {
["num_products_user_by_ref"]=>
string(1) "1"
["reference"]=>
string(3) "E49"
}
[526]=>
array(3) {
["num_products_user_by_ref"]=>
string(1) "9"
["reference"]=>
string(3) "E49"
}
[346]=>
array(3) {
["num_products_user_by_ref"]=>
string(2) "38"
["reference"]=>
string(3) "E49"
}
Every user_id could contains more than 1 pair num_products_user_by_ref/reference.
I remember that there is a function to achieve this (ksort?) associated to a custom function to implement.

Answer 1

$out = array();
foreach ($arr as $key => $value){
$out[$value['user_id']]["num_products_user_by_ref"] = $value["num_products_user_by_ref"];
$out[$value['user_id']]["reference"] = $value["reference"];
}
print_r($out);
Your question showed a structure that doesn't seem to fit with your comment "Every user_id could contains more than 1 pair num_products_user_by_ref/reference." So, here's another version that allows for that possibility:
$out = array();
foreach ($arr as $key => $value){
$entry = array("num_products_user_by_ref" => $value["num_products_user_by_ref"],
"reference" => $value["reference"]);
$out[$value['user_id']][] = $entry;
}
Output:
Array
(
[77] => Array
(
[0] => Array
(
[num_products_user_by_ref] => 1
[reference] => E49
)
[1] => Array
(
[num_products_user_by_ref] => 5
[reference] => E49
)
)
[526] => Array
(
[0] => Array
(
[num_products_user_by_ref] => 9
[reference] => E49
)
)
[346] => Array
(
[0] => Array
(
[num_products_user_by_ref] => 38
[reference] => E49
)
)
)
Here's another version for those who don't like traditional loops:
$out = array();
array_walk($arr, function($e, $k) use(&$out){
$entry = array("num_products_user_by_ref" => $e["num_products_user_by_ref"],
"reference" => $e["reference"]);
$out[$e['user_id']][] = $entry;
});