PHP take all combinations

Question

I saw this algorithm that will take numbers or words and find all possible combinations

And I'm using it, but it does NOT return all "real" combinations.

PHP:

<?php
    require_once 'Math/Combinatorics.php';
    $words = array('cat', 'dog', 'fish');
    $combinatorics = new Math_Combinatorics;
    foreach($combinatorics->permutations($words, 2) as $p) {
        echo join(' ', $p), "\n"; 
    }
?>

And it returns:

cat dog
dog cat
cat fish
fish cat
dog fish
fish dog

But these are not all real combinations, all real combinations includes these too:

cat cat
dog dog
fish fish

And that is what I need, the method to get all real combinations:

cat dog
dog cat
cat fish
fish cat
dog fish
fish dog
cat cat
dog dog
fish fish

Why don't you add these combinations yourself? Seems easy enough to loop through your data and add the pairs manually. — laurent, Mar 20 '12 at 12:49
Isn't this the same question as before? You're just having doubts on the answer it seems. why not continue there? — Nanne, Mar 20 '12 at 12:52
Math_Combinatorics - "A package that returns all the combinations and permutations, without repitition, of a given set and subset size. Associative arrays are preserved.". The key here is "without repetition". — strkol, Mar 20 '12 at 12:54
If this is just for fun, it wouldn't be hard to write your own function that would add the duplicates. If it isn't just for fun, there is probably a better way to do what you want. — jasonlfunk, Mar 20 '12 at 12:57
thats because you are using a code for permutations not combinations — Juan Antonio Orozco, Jul 10 '13 at 01:20

Dr.Kameleon · Accepted Answer · 2012-03-20T13:19:04.870

OK, here's your code (and btw, thanks for posting such an interesting and challenging problem - at least for me... :-)) - using recursion for all possible permutations (by N) given an array of elements)

Code :

<?php

function permutations($arr,$n)
{
     $res = array();

     foreach ($arr as $w)
     {
           if ($n==1) $res[] = $w;
           else
           {
                 $perms = permutations($arr,$n-1);

                 foreach ($perms as $p)
                 {
                      $res[] = $w." ".$p;
                 } 
           }
     }

     return $res;
}

// Your array
$words = array('cat','dog','fish');

// Get permutation by groups of 3 elements
$pe = permutations($words,3);

// Print it out
print_r($pe);

?>

Output :

Array
(
    [0] => cat cat cat
    [1] => cat cat dog
    [2] => cat cat fish
    [3] => cat dog cat
    [4] => cat dog dog
    [5] => cat dog fish
    [6] => cat fish cat
    [7] => cat fish dog
    [8] => cat fish fish
    [9] => dog cat cat
    [10] => dog cat dog
    [11] => dog cat fish
    [12] => dog dog cat
    [13] => dog dog dog
    [14] => dog dog fish
    [15] => dog fish cat
    [16] => dog fish dog
    [17] => dog fish fish
    [18] => fish cat cat
    [19] => fish cat dog
    [20] => fish cat fish
    [21] => fish dog cat
    [22] => fish dog dog
    [23] => fish dog fish
    [24] => fish fish cat
    [25] => fish fish dog
    [26] => fish fish fish
)

HINT : By permutations($words,2), you'll be able to get exactly what you wanted...

I'm trying to convert this to return an array of arrays instead of an array of strings. So each inner array would have $n elements in it. It's proving more difficult than it seems it should be... — still_dreaming_1, Oct 13 '16 at 23:03
Actually the Combinatorics class does help with some things, but it is different from this because it would not produce subsets with duplicate values like this solution does. I still need a version of this that works with arrays instead of strings. — still_dreaming_1, Oct 18 '16 at 20:27

score 0 · Answer 2 · answered Mar 20 '12 at 13:00

0

Your current code gives you permutations, simply add duplicates:

foreach($words as $w) {
    echo "$w $w\n";    
}

What's the problem?

answered Mar 20 '12 at 13:00

William R

185
1
10

The problem is that that is non-generic, and will not work if you are working with more then 2 dimensions: in 3 dimensions he would need to add cat cat fish, cat fish cat, fish cat cat. etc... again combinatorics. – Ellert van Koperen Jan 16 '16 at 17:54

PHP take all combinations

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