PHP Find All (somewhat) Unique Combinations of an Array

Question

I\'ve been looking at PHP array permutation / combination questions all day.. and still can\'t figure it out :/

If I have an array like:

20 //key bei         


        

Answer 1

Had the same problem and found a different and bitwise, faster solution:

function bitprint($u) {
    $s = array();
    for ($n=0; $u; $n++, $u >>= 1){
        if ($u&1){
            $s [] = $n;
        }
    }
    return $s;
}
function bitcount($u) {
    for ($n=0; $u; $n++, $u = $u&($u-1));
    return $n;
}
function comb($c,$n) {
    $s = array();
    for ($u=0; $u<1<<$n; $u++){
        if (bitcount($u) == $c){
            $s [] = bitprint($u);
        }
    }
    return $s;
}

This one generates all size m combinations of the integers from 0 to n-1, so for example m = 2, n = 3 and calling comb(2, 3) will produce:

0 1
0 2
1 2

It gives you index positions, so it's easy to point to array elements by index.

Edit: Fails with input comb(30, 5). Have no idea why, anyone any idea?

Answer 2

The Idea is simple. Suppose you know how to permute, then if you save these permutations in a set it becomes a combinations. Set by definition takes care of the duplicate values. The Php euqivalent of Set or HashSet is SplObjectStorage and ArrayList is Array. It should not be hard to rewrite. I have an implementation in Java:

public static HashSet<ArrayList<Integer>> permuteWithoutDuplicate(ArrayList<Integer> input){
          if(input.size()==1){
              HashSet<ArrayList<Integer>> b=new HashSet<ArrayList<Integer>>();
              b.add(input);
              return b;
          }
          HashSet<ArrayList<Integer>>ret= new HashSet<ArrayList<Integer>>();
          int len=input.size();
          for(int i=0;i<len;i++){
              Integer a = input.remove(i);
              HashSet<ArrayList<Integer>>temp=permuteWithoutDuplicate(new ArrayList<Integer>(input));
              for(ArrayList<Integer> t:temp)
                  t.add(a);
              ret.addAll(temp);
              input.add(i, a);
          }
          return ret;
      }

Answer 3

Cleaned up Adi Bradfield's sugestion using strrev and for/foreach loops, and only get unique results.

function search_get_combos($array = array()) {
sort($array);
$terms = array();

for ($dec = 1; $dec < pow(2, count($array)); $dec++) {
    $curterm = array();
    foreach (str_split(strrev(decbin($dec))) as $i => $bit) {
        if ($bit) {
            $curterm[] = $array[$i];
        }
    }
    if (!in_array($curterm, $terms)) {
        $terms[] = $curterm;
    }
}

return $terms;
}

Answer 4

If you don't mind using a couple of global variables, you could do this in PHP (translated from a version in JavaScript):

<?PHP
$result = array(); 
$combination = array();

function combinations(array $myArray, $choose) {
  global $result, $combination;

  $n = count($myArray);

  function inner ($start, $choose_, $arr, $n) {
    global $result, $combination;

    if ($choose_ == 0) array_push($result,$combination);
    else for ($i = $start; $i <= $n - $choose_; ++$i) {
           array_push($combination, $arr[$i]);
           inner($i + 1, $choose_ - 1, $arr, $n);
           array_pop($combination);
         }
  }
  inner(0, $choose, $myArray, $n);
  return $result;
}

print_r(combinations(array(20,20,22,24), 3));
?>

OUTPUT:

Array ( [0] => Array ( [0] => 20 
                       [1] => 20 
                       [2] => 22 ) 
        [1] => Array ( [0] => 20 
                       [1] => 20 
                       [2] => 24 ) 
        [2] => Array ( [0] => 20 
                       [1] => 22 
                       [2] => 24 ) 
        [3] => Array ( [0] => 20 
                       [1] => 22 
                       [2] => 24 ) ) 

Answer 5

The pear package Math_Combinatorics makes this kind of problem fairly easy. It takes relatively little code, it's simple and straightforward, and it's pretty easy to read.

$ cat code/php/test.php
<?php
$input = array(20, 20, 22, 24);

require_once 'Math/Combinatorics.php';

$c = new Math_Combinatorics;
$combinations = $c->combinations($input, 3);
for ($i = 0; $i < count($combinations); $i++) {
  $vals = array_values($combinations[$i]);
  $s = implode($vals, ", ");
  print $s . "\n";
}
?>

$ php code/php/test.php
20, 20, 22
20, 20, 24
20, 22, 24
20, 22, 24

If I had to package this as a function, I'd do something like this.

function combinations($arr, $num_at_a_time) 
{
    include_once 'Math/Combinatorics.php';

    if (count($arr) < $num_at_a_time) {
        $arr_count = count($arr);
        trigger_error(
            "Cannot take $arr_count elements $num_at_a_time " 
            ."at a time.", E_USER_ERROR
        );
    }

    $c = new Math_Combinatorics;
    $combinations = $c->combinations($arr, $num_at_a_time);

    $return = array();
    for ($i = 0; $i < count($combinations); $i++) {
        $values = array_values($combinations[$i]);
        $return[$i] = $values;
    }
    return $return;
}

That will return an array of arrays. To get the text . . .

<?php
  include_once('combinations.php');

  $input = array(20, 20, 22, 24);
  $output = combinations($input, 3);

  foreach ($output as $row) {
      print implode($row, ", ").PHP_EOL;
  }
?>
20, 20, 22
20, 20, 24
20, 22, 24
20, 22, 24

Answer 6

Why not just use binary? At least then its simple and very easy to understand what each line of code does like this? Here's a function i wrote for myself in a project which i think is pretty neat!

function search_get_combos($array){
$bits = count($array); //bits of binary number equal to number of words in query;
//Convert decimal number to binary with set number of bits, and split into array
$dec = 1;
$binary = str_split(str_pad(decbin($dec), $bits, '0', STR_PAD_LEFT));
while($dec < pow(2, $bits)) {
    //Each 'word' is linked to a bit of the binary number.
    //Whenever the bit is '1' its added to the current term.
    $curterm = "";
    $i = 0;
    while($i < ($bits)){
        if($binary[$i] == 1) {
            $curterm[] = $array[$i]." ";
        }
        $i++;
    }
    $terms[] = $curterm;
    //Count up by 1
    $dec++;
    $binary = str_split(str_pad(decbin($dec), $bits, '0', STR_PAD_LEFT));
}
return $terms;
} 

For your example, this outputs:

Array
(
    [0] => Array
        (
            [0] => 24 
        )
    [1] => Array
        (
            [0] => 22 
        )
    [2] => Array
        (
            [0] => 22 
            [1] => 24 
        )
    [3] => Array
        (
            [0] => 20 
        )
    [4] => Array
        (
            [0] => 20 
            [1] => 24 
        )
    [5] => Array
        (
            [0] => 20 
            [1] => 22 
        )
    [6] => Array
        (
            [0] => 20 
            [1] => 22 
            [2] => 24 
        )
    [7] => Array
        (
            [0] => 20 
        )
    [8] => Array
        (
            [0] => 20 
            [1] => 24 
        )
    [9] => Array
        (
            [0] => 20 
            [1] => 22 
        )
    [10] => Array
        (
            [0] => 20 
            [1] => 22 
            [2] => 24 
        )
    [11] => Array
        (
            [0] => 20 
            [1] => 20 
        )
    [12] => Array
        (
            [0] => 20 
            [1] => 20 
            [2] => 24 
        )
    [13] => Array
        (
            [0] => 20 
            [1] => 20 
            [2] => 22 
        )
    [14] => Array
        (
            [0] => 20 
            [1] => 20 
            [2] => 22 
            [3] => 24 
        )
)