How to Get All Possible Pairs in Array using PHP ?

Given an array containing some elements, the task is to find all possible pairs of array elements using PHP.

Examples:

Input: arr = [1, 2, 3]
Output: [[1, 2], [1, 3]]

Input: arr = [1, 2, 3, 5]
Output: [[1, 2], [1, 3], [1, 5], [2, 3], [2, 5], [3, 5]]

Approach 1: Using Nested for Loops

Nested loop is the most straightforward method to find all possible pairs in an array. This method involves iterating through the array with two loops and selecting unique pairs of elements

Example:

PHP

<?php

function getAllPairs($arr) {
    $pairs = [];

    $len = count($arr);

    for ($i = 0; $i < $len - 1; $i++) {
        for ($j = $i + 1; $j < $len; $j++) {
            $pairs[] = [$arr[$i], $arr[$j]];
        }
    }

    return $pairs;
}

// Driver code
$arr = [1, 2, 3, 4, 5];
$pairs = getAllPairs($arr);

print_r($pairs);

?>

Output:

Array (
    [0] => Array(
        [0] => 1
        [1] => 2
    )
    [1] => Array(
        [0] => 1
        [1] => 3
    )
    [2] => Array(
        [0] => 1
        [1] => 4
    )
    [3] => Array(
        [0] => 1
        [1] => 5
    )
    [4] => Array(
        [0] => 2
        [1] => 3
    )
    [5] => Array(
        [0] => 2
        [1] => 4
    )
    [6] => Array(
        [0] => 2
        [1] => 5
    )
    [7] => Array(
        [0] => 3
        [1] => 4
    )
    [8] => Array(
        [0] => 3
        [1] => 5
    )
    [9] => Array(
        [0] => 4
        [1] => 5
    )
)

Approach 2: Using array_reduce() Function

The array_reduce() function can be used to generate all possible pairs. This approach involves iterating through the array and creating pairs using a combination of array_map() and array_slice() functions.

Example:

PHP

<?php

function getAllPairs($arr) {
    $pairs = array_reduce($arr,
        function ($result, $item1) use ($arr) {

        $pairs = array_map(
            function ($item2) use ($item1) {
                return [$item1, $item2];
            }, array_slice($arr,
            array_search($item1, $arr) + 1)
        );

        return array_merge($result, $pairs);
    }, []);

    return $pairs;
}

// Driver code
$arr = [1, 2, 3, 4, 5];
$pairs = getAllPairs($arr);

print_r($pairs);

?>

Output

Array
(
    [0] => Array
        (
            [0] => 1
            [1] => 2
        )

    [1] => Array
        (
            [0] => 1
            [1] => 3
        )

    [2] => Array
        (
     ...