Generate all combinations of a specific size from a single set in PHP

To generate all combinations of a specific size from a single set, the code is as follows −

Example

 Live Demo

function sampling($chars, $size, $combinations = array()) {
   # in case of first iteration, the first set of combinations is the same as the set of characters
   if (empty($combinations)) {
      $combinations = $chars;
   }
   # size 1 indicates we are done
   if ($size == 1) {
      return $combinations;
   }
   # initialise array to put new values into it
   $new_combinations = array();
   # loop through the existing combinations and character set to create strings
   foreach ($combinations as $combination) {
      foreach ($chars as $char) {
         $new_combinations[] = $combination . $char;
      }
   }
   # call the same function again for the next iteration as well
   return sampling($chars, $size - 1, $new_combinations);
}
$chars = array('a', 'b', 'c');
$output = sampling($chars, 2);
var_dump($output);

Output

This will produce the following output −

array(9) { [0]=> string(2) "aa" [1]=> string(2) "ab" [2]=> string(2) "ac" [3]=> string(2) "ba" [4]=> string(2) "bb" [5]=> string(2) "bc" [6]=> string(2) "ca" [7]=> string(2) "cb" [8]=> string(2) "cc" }

The first iteration indicates the same set of characters to be displayed. If the size is 1, then the combination is displayed. An array is initialized as ‘new_combinations’ and it is looped through using the ‘forloop’ and every character in that string is concatenated with every other character. The function ‘sampling’ is called with the parameters (string, the size of the string and the array).