README

String combinations

A simple, low-memory footprint function to generate all string combinations from a series of characters.

Installation

PHP 7.4+ is required.

composer require bentools/string-combinations

Usage

I want to get all combinations with the letters a, b, c.

require_once __DIR__ . '/vendor/autoload.php'; use function BenTools\StringCombinations\string_combinations; foreach (string_combinations('abc') as $combination) { // Can also be string_combinations(['a', 'b', 'c']) echo $combination . PHP_EOL; }

Output:

a b c aa ab ac ba bb bc ca cb cc aaa aab aac aba abb abc aca acb acc baa bab bac bba bbb bbc bca bcb bcc caa cab cac cba cbb cbc cca ccb ccc 

Array output

It will dump all combinations into an array.

var_dump(string_combinations('abc')->asArray());

Count combinations

It will return the number of possible combinations.

var_dump(count(string_combinations('abc'))); // 39

Specifying min length, max length

foreach (string_combinations('abc', $min = 2, $max = 2) as $combination) { echo $combination . PHP_EOL; }

Output:

aa ab ac ba bb bc ca cb cc 

Using an array as first argument, and a separator

foreach (string_combinations(['woof', 'meow', 'roar'], 2, 3, '-') as $combination) { echo $combination . PHP_EOL; }

Output:

woof-woof woof-meow woof-roar meow-woof meow-meow meow-roar roar-woof roar-meow roar-roar woof-woof-woof woof-woof-meow woof-woof-roar woof-meow-woof woof-meow-meow woof-meow-roar woof-roar-woof woof-roar-meow woof-roar-roar meow-woof-woof meow-woof-meow meow-woof-roar meow-meow-woof meow-meow-meow meow-meow-roar meow-roar-woof meow-roar-meow meow-roar-roar roar-woof-woof roar-woof-meow roar-woof-roar roar-meow-woof roar-meow-meow roar-meow-roar roar-roar-woof roar-roar-meow roar-roar-roar 

No duplicates

You can avoid generating stings having the same letter more than once with the withoutDuplicates() method:

$combinations = string_combinations('abc'); var_dump(count($combinations)); // 39 print_r($combinations->asArray());

Array ( [0] => a [1] => b [2] => c [3] => aa [4] => ab [5] => ac [6] => ba [7] => bb [8] => bc [9] => ca [10] => cb [11] => cc [12] => aaa [13] => aab [14] => aac [15] => aba [16] => abb [17] => abc [18] => aca [19] => acb [20] => acc [21] => baa [22] => bab [23] => bac [24] => bba [25] => bbb [26] => bbc [27] => bca [28] => bcb [29] => bcc [30] => caa [31] => cab [32] => cac [33] => cba [34] => cbb [35] => cbc [36] => cca [37] => ccb [38] => ccc )

$combinations = $combinations->withoutDuplicates(); var_dump(count($combinations)); // 15 print_r($combinations->asArray());

Array ( [0] => a [1] => b [2] => c [3] => ab [4] => ac [5] => ba [6] => bc [7] => ca [8] => cb [9] => abc [10] => acb [11] => bac [12] => bca [13] => cab [14] => cba )

Performance considerations

Because it uses Generators to generate all possible combinations, you can iterate over thousands of possibilities without losing a single MB.

This has been executed on my Core i7 personnal computer with 8GB RAM:

require_once __DIR__ . '/vendor/autoload.php'; use function BenTools\StringCombinations\string_combinations; $start = microtime(true); $combinations = string_combinations('abcd1234'); foreach ($combinations as $c => $combination) { continue; } $end = microtime(true); printf( 'Generated %d combinations in %ss - Memory usage: %sMB / Peak usage: %sMB' . PHP_EOL, ++$c, round($end - $start, 3), round(memory_get_usage(true) / 1024 / 1024), round(memory_get_peak_usage(true) / 1024 / 1024) );

Output:

Generated 19173960 combinations in 5.579s - Memory usage: 2MB / Peak usage: 2MB

Tests

./vendor/bin/phpunit

See also

• bentools/cartesian-product
• bentools/iterable-functions