Find combination of array keys with values - php

Question

In order to optimize the output I recently ran into a situation where I have to get the all the combinations of array keys inside an array. I looked into several places (including StackOverflow) but could not find the solution since most are related to permutation rather than combination.
Given this input
$input = ['jack' => 11, 'moe' => 12, 'shane' => 12];
Output should be something like this (the order inside an array does not matter).
$output = [
['jack' => 11],
['jack' => 11, 'moe' => 12]
['jack' => 11, 'moe' => 12, 'shane' => 12]
['moe' => 12],
['moe' => 12, 'shane' => 12]
['shane' => 12],
['shane' => 12, 'jack' => 11]
];
I tried this but after third iteration it does not work.
function combination(array $inputs, array $temp, &$collect) {
if (!empty($temp)) {
$collect[] = $temp;
}
for ($i = 0; $i < sizeof($inputs); $i++) {
$inputCopy = $inputs;
$elem = array_splice($inputCopy, $i, 1);
if (count($inputCopy) > 0) {
$temp[array_keys($elem)[0]] = array_values($elem)[0];
combination($inputCopy, $temp, $collect);
} else {
$temp[array_keys($elem)[0]] = array_values($elem)[0];
$collect[] = $temp;
$temp = [];
}
$i++;
}
}
Though I need this in PHP even Python (without using itertools combination), Java, Javascript will work for me.

Answer 1

I have found a way of doing what you want, but definitely, this is not a "fancy" solution. I would suggest you to work a little bit with it to find something better, but at least this gives you the result.
Here you go :
<?php
$baseArray = [
"joe" => 11,
"molly" => 12,
"sam" => 13,
];
function getAllPermutations($array = []) {
if (empty($array)) {
return [];
}
$result = [];
foreach ($array as $key => $value) {
unset($array[$key]);
$subPermutations = getAllPermutations($array);
$result[] = [$key => $value];
foreach ($subPermutations as $sub) {
$result[] = array_merge([$key => $value] , $sub);
}
}
return $result;
}
print_r(getAllPermutations($baseArray));
Output being :
Array
(
[0] => Array
(
[joe] => 11
)
[1] => Array
(
[joe] => 11
[molly] => 12
)
[2] => Array
(
[joe] => 11
[molly] => 12
[sam] => 13
)
[3] => Array
(
[joe] => 11
[sam] => 13
)
[4] => Array
(
[molly] => 12
)
[5] => Array
(
[molly] => 12
[sam] => 13
)
[6] => Array
(
[sam] => 13
)
) }
Hope this helped.

Answer 2

You read about really clever non-recursive algorithm here: PHP: Find every combination of an Array. You can adopt it (mostly copy and paste) to write generator function:
function keyCombinations($array)
{
$keys = array_keys($array);
$num = count($keys);
$total = pow(2, $num);
for ($i = 1; $i < $total; $i++) {
$combination = [];
for ($j = 0; $j < $num; $j++) {
if (pow(2, $j) & $i) {
$key = $keys[$j];
$combination[$key] = $array[$key];
}
}
yield $combination;
}
}
One important point here. In the original article $i initialized with 0, we initialize it with 1 to exclude empty array from the result.
Having this function you can get all combinations:
foreach (keyCombinations($input) as $combination) {
print_r($combination);
}
Here is working demo.

Answer 3

If, in your final combination, you include the empty set, your problem is equivalent to enumerating a binary number of "n" bits. Where "n" is the number of elements in your set.
You need a recursive algorithm like this one:
def comb(initialSet, results=[], currentIndex=0, currentResult=[]):
if currentIndex >= len(initialSet):
results.append( currentResult[:] )
else:
currentResult.append( initialSet[currentIndex] )
comb(initialSet, results, currentIndex + 1, currentResult)
currentResult.pop()
comb(initialSet, results, currentIndex + 1, currentResult)
return results