up vote 8 down vote favorite
4

I've had this problem bending my mind for a while now (head cold doesn't help either!), basically I have a PHP array which looks like this example:

$array[0][0] = 'apples';
$array[0][1] = 'pears';
$array[0][2] = 'oranges';

$array[1][0] = 'steve';
$array[1][1] = 'bob';

And I would like to be able to produce from this a table with every possible combination of these, but without repeating any combinations (regardless of their position), so for example this would output

Array 0            Array 1
apples             steve
apples             bob
pears              steve
pears              bob

But I would like for this to be able to work with as many different arrays as possible.

Many thanks!

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Will there be Array 2, Array 3, Array N? Or only two arrays? – Silver Light Mar 25 '10 at 15:05
Hi sorry for not making clearer, there could be array 2, array 3 up to array n. Thanks. – stukerr Mar 25 '10 at 15:05
What you need is a cross join done easy in SQL, but needs some thinking in PHP – Silver Light Mar 25 '10 at 15:15
As it happens this is coming from a mySQL database, all the options (apples, pears, oranges, steve, bob, etc.) are in one table kit a key to another table defining which group they are in (fruits, people etc.), any ideas how I could work that in mysql ? – stukerr Mar 25 '10 at 15:20
1  
duplicate of : stackoverflow.com/questions/2516599/… – Foo Bah Feb 9 '11 at 20:35
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8 Answers

up vote 7 down vote accepted

this is called "cartesian product", php man page on arrays http://php.net/manual/en/ref.array.php shows some implementations (in comments).

and here's yet another one:

function array_cartesian() {
    $_ = func_get_args();
    if(count($_) == 0)
        return array(array());
    $a = array_shift($_);
    $c = call_user_func_array(__FUNCTION__, $_);
    $r = array();
    foreach($a as $v)
        foreach($c as $p)
            $r[] = array_merge(array($v), $p);
    return $r;
}

$cross = array_cartesian(
    array('apples', 'pears',  'oranges'),
    array('steve', 'bob')
);

print_r($cross);
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Great stuff, just what I needed. Many thanks – stukerr Mar 25 '10 at 16:13
lets put the real page there: php.net/manual/en/ref.array.php :) – Foo Bah Feb 9 '11 at 22:07
If this function lives in a class, you might want to change the user_func call like so: $c = call_user_func_array(array($this,__FUNCTION__), $_);. Also, it can give a warning (not an array) if input-arrays aren't of equal size. – Nanne Aug 21 at 14:43
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up vote 4 down vote

You are looking for the cartesian product of the arrays, and there's an example on the php arrays site: http://php.net/manual/en/ref.array.php

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up vote 1 down vote 
foreach($parentArray as $value) {
    foreach($subArray as $value2) {
        $comboArray[] = array($value, $value2); 
    }
}

Don't judge me..

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"Of course it must work when sizeof($array) >= 2." – Rob Kennedy Feb 9 '11 at 20:46
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up vote 1 down vote

I modified this to be

function array_cartesian() {
    $_ = func_get_args();
    if (count($_) == 0)
        return array();
    $a = array_shift($_);
    if (count($_) == 0)
        $c = array(array());
    else
        $c = call_user_func_array(__FUNCTION__, $_);
    $r = array();
    foreach($a as $v)
        foreach($c as $p)
            $r[] = array_merge(array($v), $p);
    return $r;
}

so it returns that all-important empty array (the same result as no combinations) when you pass 0 arguments.

Only noticed this because I'm using it like

$combos = call_user_func_array('array_cartesian', $array_of_arrays);
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up vote 1 down vote

This works I think - although after writing it I realised it's pretty similar to what others have put, but it does give you an array in the format requested. Sorry for the poor variable naming.

$output = array();
combinations($array, $output);
print_r($output);

function combinations ($array, & $output, $index = 0, $p = array()) {
    foreach ( $array[$index] as $i => $name ) {
        $copy = $p;
        $copy[] = $name;
        $subIndex = $index + 1;
        if (isset( $array[$subIndex])) {
            combinations ($array, $output, $subIndex, $copy);
        } else {
            foreach ($copy as $index => $name) {
                if ( !isset($output[$index])) {
                    $output[$index] = array();   
                }
                $output[$index][] = $name;   
            }
        }
    }
}
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up vote 1 down vote

Syom copied http://www.php.net/manual/en/ref.array.php#54979 but I adapted it this to become an associative version:

function array_cartesian($arrays) {
  $result = array();
  $keys = array_keys($arrays);
  $reverse_keys = array_reverse($keys);
  $size = intval(count($arrays) > 0);
  foreach ($arrays as $array) {
    $size *= count($array);
  }
  for ($i = 0; $i < $size; $i ++) {
    $result[$i] = array();
    foreach ($keys as $j) {
      $result[$i][$j] = current($arrays[$j]);
    }
    foreach ($reverse_keys as $j) {
      if (next($arrays[$j])) {
        break;
      }
      elseif (isset ($arrays[$j])) {
        reset($arrays[$j]);
      }
    }
  }
  return $result;
}
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up vote 0 down vote

In MySQL database in would be like this:

SELECT *
FROM `options`, `groups`

That's all :)

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up vote 0 down vote 
function array_comb($arrays)
{
    $result = array();
    $arrays = array_values($arrays);
    $sizeIn = sizeof($arrays);
    $size = $sizeIn > 0 ? 1 : 0;
    foreach ($arrays as $array)
        $size = $size * sizeof($array);
    for ($i = 0; $i < $size; $i ++)
    {
        $result[$i] = array();
        for ($j = 0; $j < $sizeIn; $j ++)
            array_push($result[$i], current($arrays[$j]));
        for ($j = ($sizeIn -1); $j >= 0; $j --)
        {
            if (next($arrays[$j]))
                break;
            elseif (isset ($arrays[$j]))
                reset($arrays[$j]);
        }
    }
    return $result;
}
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