'All combinations of r elements from given array php

Given an array such as the following

$array = ('1', '2', '3', '4', '5', '6', '7');

I'm looking for a method to generate all possible combinations, with a minimum number of elements required in each combination r. (eg if r = 5 then it will return all possible combinations containing at least 5 elements)

phparrayscombinations


Solution 1:[1]

Combinations of k out of n items can be defined recursively using the following function:

function combinationsOf($k, $xs){
        if ($k === 0)
            return array(array());
        if (count($xs) === 0)
            return array();
        $x = $xs[0];
        $xs1 = array_slice($xs,1,count($xs)-1);
        $res1 = combinationsOf($k-1,$xs1);
        for ($i = 0; $i < count($res1); $i++) {
            array_splice($res1[$i], 0, 0, $x);
        }
        $res2 = combinationsOf($k,$xs1);
        return array_merge($res1, $res2);
    }

The above is based on the recursive definition that to choose k out n elements, one can fix an element x in the list, and there are C(k-1, xs\{x}) combinations that contain x (i.e. res1), and C(k,xs\{xs}) combinations that do not contain x (i.e. res2 in code).

Full example:

$array = array('1', '2', '3', '4', '5', '6', '7');

function combinationsOf($k, $xs){
        if ($k === 0)
            return array(array());
        if (count($xs) === 0)
            return array();
        $x = $xs[0];
        $xs1 = array_slice($xs,1,count($xs)-1);
        $res1 = combinationsOf($k-1,$xs1);
        for ($i = 0; $i < count($res1); $i++) {
            array_splice($res1[$i], 0, 0, $x);
        }
        $res2 = combinationsOf($k,$xs1);
        return array_merge($res1, $res2);
    }

print_r ($array);
print_r(combinationsOf(5,$array));
//print_r(combinationsOf(5,$array)+combinationsOf(6,$array)+combinationsOf(7,$array));

Solution 2:[2]

    function arrToBit(Array $element) {
        $bit = '';
        foreach ($element as $e) {
            $bit .= '1';
        }
        $length = count($element);
        $num = bindec($bit);
        $back = [];
        while ($num) {
            $back[] = str_pad(decbin($num), $length, '0', STR_PAD_LEFT);
            $num--;
        }
        //$back[] = str_pad(decbin(0), $length, '0', STR_PAD_LEFT);
        return $back;
    }

    function bitToArr(Array $element, $bit) {
        $num = count($element);
        $back = [];
        for ($i = 0; $i < $num; $i++) {
            if (substr($bit, $i, 1) == '1') {
                $back[] = $element[$i];
            }
        }
        return $back;
    }

    $tags = ['a', 'b', 'c'];
    $bits = arrToBit($tags);
    $combination = [];
    foreach ($bits as $b) {
        $combination[] = bitToArr($tags, $b);
    }
    var_dump($combination);

Solution 3:[3]

$arr = array(1,2,3,4,5,6);
$check_value =[];
$all_values = [];
CONT:
$result = $check_value;
shuffle($arr);
$check_value = array_slice($arr,0,3);
if(count($check_value) == 3 && serialize($check_value) !== serialize($result)){
$result = $check_value;
array_push($all_values,$result);
goto CONT;
}

print_r($all_values);

Sources

This article follows the attribution requirements of Stack Overflow and is licensed under CC BY-SA 3.0.

Source: Stack Overflow

Solution Source
Solution 1
Solution 2 James Zhu
Solution 3 Ranjan Baitha

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