php - Generating all combinations of possible clicked checkboxes to add the values -

i have generate possible combinations of 4 checkboxes order not matter. reason order not matter because add values connected checkboxes.

the array of categories is: ['kw1','kw2','kw3','kw4']

this means kw1+kw2 = kw2+kw1. must seen 1 combination.

i've gotten pretty far, failing wrap head around it.

first of all, user can click between 1 , 4 checkboxes, there no fixed amount of checked checkboxes required. can translated loop:

for($i=1;$i<=4;$i++){  } 

when 1 checkbox can clicked, there 4 possible options. when 4 checkboxes checked, 1 option available. when 1st checkbox checked, there 3 options left. when 2nd checkbox checked, 2 options remain available. drill.

i translated to:

for($i=1;$i<=4;$i++){     $j = 5 - $i;     $reverse_j = 0;     $categories = array('kw1','kw2','kw3','kw4');     for($j;$j>0;$j--){         $reverse_j++;         $counter = 0;         foreach($categories $category){             $counter++;             $tmp = $categories;             if($counter <= $i){                 $result[$i][$reverse_j][] = $tmp[0];                 unset($tmp[0]);                 $tmp = array_values($tmp);             }         }         unset($categories[0]);         $categories = array_values($categories);     } } 

the above 1 of many failed attempts trying generate combinations. i've written out combinations, because not hard, want create code it.

the possible combinations should be:

1 click = (1), (2), (3), (4) 2 clicks = (1-2), (1-3), (1-4), (2-3) ,(2-4), (3-4) 3 clicks = (1-2-3), (1-2-4), (1-3-4), (2-3-4)  4 clicks = (1-2-3-4) 

what missing? thinking go wrong?

thanks comment of @dr_debug, found right term looking for: 'powerset'.

with term found following post: power set elements of length

this gave me following functions:

function subsets_n($arr, $k) {   if (count($arr) < $k) return array();   if (count($arr) == $k) return array(0 => $arr);    $x = array_pop($arr);   if (is_null($x)) return array();    return array_merge(subsets_n($arr, $k),                      merge_into_each($x, subsets_n($arr, $k-1)) ); }  function merge_into_each($x, $arr) {   foreach ($arr &$a) array_push($a, $x);   return $arr; } 

with these functions, can generate array possible combinations!