Finding the subsets of an array in PHP

You wish for the power set of $attributes? That is what your question implies.

An example can be found here (quoted for completeness)

<?php /** * Returns the power set of a one dimensional array, a 2-D array. * [a,b,c] -> [ [a], [b], [c], [a, b], [a, c], [b, c], [a, b, c] ]*/ function powerSet($in,$minLength = 1) {    $count = count($in);    $members = pow(2,$count);    $return = array();    for ($i = 0; $i < $members; $i++) {       $b = sprintf("%0".$count."b",$i);       $out = array();       for ($j = 0; $j < $count; $j++) {          if ($b{$j} == '1') $out[] = $in[$j];       }       if (count($out) >= $minLength) {          $return[] = $out;       }    }    return $return; } 

Using php array_merge we can have a nice short powerSet function

function powerSet($array) {    // add the empty set    $results = [[]];    foreach ($array as $element) {        foreach ($results as $combination) {            $results[] = array_merge(array($element), $combination);        }    }    return $results;}

Here a backtracking solution.

given a function that returns all the L-lenght subsets of the input set, find all the L-lenght subsets from L = 2 to dataset input length

<?phpfunction subsets($S,$L) {    $a = $b = 0;    $subset = [];    $result = [];    while ($a < count($S)) {        $current = $S[$a++];        $subset[] = $current;        if (count($subset) == $L) {            $result[] = json_encode($subset);            array_pop($subset);        }        if ($a == count($S)) {            $a = ++$b;            $subset = [];        }    }    return $result;}$S = [ 'A', 'B', 'C', 'D'];$L = 2;// L = 1 -> no need to do anythingprint_r($S);for ($i = 2; $i <= count($S); $i++)    print_r(subsets($S,$i));