PHP: Nested loop with only unique pairs - php

Question

I need to create an array of only unique pairs so there are no duplicates.
The problem is that when just iterating over each other, for some reason last pair usually is duplicate.
So here's a quick example:
<?php
$teams = [
['id' => 1],
['id' => 2],
['id' => 3],
['id' => 4],
];
foreach ($teams as $team_a) {
foreach ($teams as $team_b) {
if ($team_a['id'] !== $team_b['id']) {
$pairs[] = [$team_a['id'], $team_b['id']];
}
}
}
?>
Returns something like this:
0: [1, 2]
1: [1, 3]
2: [1, 4]
3: [2, 1]
4: [2, 3]
5: [2, 4]
6: [3, 1]
7: [3, 2]
8: [3, 4]
...
So you can see that some pairs are the same, like [1, 2] and [2, 1]. And after the half iterations there are only repeats.
What would be the most efficient way to iterate like this and be sure that there are only unique pairs?
Thanks!

Answer 1

Obviously the duplicate always appears when key(team_a) > key(team_b)
<?php
$teams = [
['id' => 1],
['id' => 2],
['id' => 3],
['id' => 4],
];
foreach ($teams as $offset => $team_a) {
foreach (array_slice($teams, $offset+1) as $team_b) {
$pairs[] = [$team_a['id'], $team_b['id']];
}
}

Answer 2

You could to do this with recursion instead of two for each loops.
<?php
$teams = [1, 2, 3, 4, 5, 6, 7, 8, 9 , 10];
getMatchup($teams);
function getMatchUp($teams, $matches = [], $start = 0) {
// Check if the whole array has been checked
if ($start == count($teams)) {
return var_dump($matches);
}
// Check every option considering a certain start point
for ($x = $start; $x < count($teams); $x++) {
// As long the team is not the same, add to matches
if ($start !== $x) {
$matches[] = [$teams[$start] => $teams[$x]];
}
}
// First team has been matched up, start matching the second team and so on..
getMatchup($teams,$matches, $start + 1);
}
Running example:
http://sandbox.onlinephpfunctions.com/code/4277d966c4ceacdbe7024d14fb03fe05fd760471