Permutations - all possible sets of numbers
Since PHP 5.5 you can use Generators. Generators save a lot of memory and are way faster (more than half compared to pc_permute()). So if you have any chance of having PHP 5.5 installed, you definitely want Generators. This snipped is ported from Python: https://stackoverflow.com/a/104436/3745311
function permutations(array $elements)
{
if (count($elements) <= 1) {
yield $elements;
} else {
foreach (permutations(array_slice($elements, 1)) as $permutation) {
foreach (range(0, count($elements) - 1) as $i) {
yield array_merge(
array_slice($permutation, 0, $i),
[$elements[0]],
array_slice($permutation, $i)
);
}
}
}
}
Sample usage:
$list = ['a', 'b', 'c'];
foreach (permutations($list) as $permutation) {
echo implode(',', $permutation) . PHP_EOL;
}
Output:
a,b,c
b,a,c
b,c,a
a,c,b
c,a,b
c,b,a
I've something that You may like
function combination_number($k,$n){
$n = intval($n);
$k = intval($k);
if ($k > $n){
return 0;
} elseif ($n == $k) {
return 1;
} else {
if ($k >= $n - $k){
$l = $k+1;
for ($i = $l+1 ; $i <= $n ; $i++)
$l *= $i;
$m = 1;
for ($i = 2 ; $i <= $n-$k ; $i++)
$m *= $i;
} else {
$l = ($n-$k) + 1;
for ($i = $l+1 ; $i <= $n ; $i++)
$l *= $i;
$m = 1;
for ($i = 2 ; $i <= $k ; $i++)
$m *= $i;
}
}
return $l/$m;
}
function array_combination($le, $set){
$lk = combination_number($le, count($set));
$ret = array_fill(0, $lk, array_fill(0, $le, '') );
$temp = array();
for ($i = 0 ; $i < $le ; $i++)
$temp[$i] = $i;
$ret[0] = $temp;
for ($i = 1 ; $i < $lk ; $i++){
if ($temp[$le-1] != count($set)-1){
$temp[$le-1]++;
} else {
$od = -1;
for ($j = $le-2 ; $j >= 0 ; $j--)
if ($temp[$j]+1 != $temp[$j+1]){
$od = $j;
break;
}
if ($od == -1)
break;
$temp[$od]++;
for ($j = $od+1 ; $j < $le ; $j++)
$temp[$j] = $temp[$od]+$j-$od;
}
$ret[$i] = $temp;
}
for ($i = 0 ; $i < $lk ; $i++)
for ($j = 0 ; $j < $le ; $j++)
$ret[$i][$j] = $set[$ret[$i][$j]];
return $ret;
}
Here is how to use it:
To get the number of combinations:
combination_number(3,10); // returns number of combinations of ten-elements set.
To get all possible combinations:
$mySet = array("A","B","C","D","E","F");
array_combination(3, $mySet); // returns all possible combinations of 3 elements of six-elements set.
Hope You make use of that.
You're looking for the permutations formula:
nPk = n!/(n-k)!
In your case, you have 9 entries and you want to choose all of them, that's 9P9 = 9! = 362880
You can find a PHP algorithm to permutate in recipe 4.26 of O'Reilly's "PHP Cookbook".
pc_permute(array(0, 1, 2, 3, 4, 5, 7, 8));
Copied in from O'Reilly:
function pc_permute($items, $perms = array( )) {
if (empty($items)) {
print join(' ', $perms) . "\n";
} else {
for ($i = count($items) - 1; $i >= 0; --$i) {
$newitems = $items;
$newperms = $perms;
list($foo) = array_splice($newitems, $i, 1);
array_unshift($newperms, $foo);
pc_permute($newitems, $newperms);
}
}
}
Since this question often comes up in Google Search results, here's a modified version of the accepted answer that returns all combinations in an array and passes them as a return value of the function.
function pc_permute($items, $perms = array( )) {
if (empty($items)) {
$return = array($perms);
} else {
$return = array();
for ($i = count($items) - 1; $i >= 0; --$i) {
$newitems = $items;
$newperms = $perms;
list($foo) = array_splice($newitems, $i, 1);
array_unshift($newperms, $foo);
$return = array_merge($return, pc_permute($newitems, $newperms));
}
}
return $return;
}
To use:
$value = array('1', '2', '3');
print_r(pc_permute($value));