Delete double entries from array - php

Question

I have the following array in php:
[0] => Array(
(
[post_id] => 492,
[user_id] => 1
)
[1] => Array(
(
[post_id] => 501,
[user_id] => 1
)
[2] => Array(
(
[post_id] => 568,
[user_id] => 13
)
[3] => Array(
(
[post_id] => 897,
[user_id] => 13
)
What I want to do, is to delete the ones where the user_id already exists. So the result should look like this:
[0] => Array(
(
[post_id] => 492,
[user_id] => 1
)
[1] => Array(
(
[post_id] => 568,
[user_id] => 13
)
I need an array, in which every user_id only exists one time.
array_unique() doesn't work for this example. Any ideas?
Thanks!

Answer 1

You can loop through and find unique values as you go:
$exists = array();
foreach($items as $key => $item) {
if(!in_array($item['user_id'], $exists)) {
$exists[] = $item['user_id'];
} else {
unset($items[$key]);
}
}
This will unset any arrays that already exist in the $exists array.

Answer 2

Here is the easy function to solve the issue.
$array = Array();
$array[] = Array('post_id'=>492 , 'user_id' => '1');
$array[] = Array('post_id'=>501 , 'user_id' => '1');
$array[] = Array('post_id'=>568 , 'user_id' => '13');
$array[] = Array('post_id'=>897 , 'user_id' => '13');
print_r($array);
print_r(make_unique_by_key($array,'user_id'));
function make_unique_by_key($m_arr , $key) {
$tmp_arr = array();
foreach ($m_arr as &$item) {
if (!isset($tmp_arr[$item[$key]])) {
$tmp_arr[$item[$key]] =& $item;
}
}
$ret_arr = array_values($tmp_arr);
return $ret_arr;
}