Friends highscore: merging two arrays - php

Question

I'm developing a game on Facebook and want to show the users a friends highscore.
What's the most efficient way to do this?
I have two arrays:
The first one, $all, coming from my database, holds the fbid's and the score's of ALL users who played the game:
Array
(
[0] => Array
(
[uid] => 12345
[score] => 0
[endgame] => 1404316845
)
[1] => Array
(
[uid] => 112873
[score] => 0
[endgame] => 1404334512
)
...
)
The second one, $friends, coming from Facebook, holds ALL the user's friends:
Array
(
[0] => Array
(
[uid] => 12345
[name] => Some Name
[pic_square] => https://...
)
[1] => Array
(
[uid] => 43324324
[name] => Another Name
[pic_square] => https://...
)
[2] => Array
(
[uid] => 4893424242
[name] => Yet Another
[pic_square] => https://...
)
...
)
I think the prefered method here is to generate an new array, which contains only friends who played the game and have a score, like this:
Array
(
[0] => Array
(
[uid] => 12345
[name] => Some Name
[pic_square] => https://...
[score] => 0
[endgame] => 1404316845
)
...
)
I've tried various things using in_array, but can't get it right... Anyone who can help me?

Answer 1

Create a new array for the scores that is indexed by uid.
$indexedScores = [];
foreach($all as $score) {
$indexedScores[$score['uid']] = $score['score'];
}
Then loop through the friends array and set the score by looking up $indexedScores
foreach($friends as $key => &$friend) {
if(isset($indexedScores[$friend['uid']])) {
$friend['score'] = $indexedScores[$friend['uid']];
}
else {
unset($friends[$key]); //doesn't have a score, so remove
}
}
usort($friends, function($a, $b) {
return $a['score'] > $b['score'];
});