Concatenate the values from one array to another in PHP - php

Question

I am trying to create a function to generate all the possible combinations of a particular group of characters, and have it variable based on length.
I have a function to create an array of the characters I would like, and this works fine.
function generate_characters($l, $n, $d) {
$r = array();
if ($l === true) {
foreach (range('a', 'z') as $index) {
array_push($r, $index);
}
}
if ($n === true) { array_push($r, '0','1','2','3','4','5','6','7','8','9'); }
if ($d === true) { array_push($r, '-'); }
return $r;
}
I then need to have it create an array of all possible combinations based on $length, for example if '$length = 1' I need the following array
Array
(
[0] => a
[1] => b
[2] => c
[3] => d
[4] => e
[5] => f
[6] => g
[7] => h
[8] => i
[9] => j
[10] => k
[11] => l
[12] => m
[13] => n
[14] => o
[15] => p
[.... removed some values to save on length ....]
[35] => 9
)
but if '$length = 2' I need this
Array
(
[0] => aa
[1] => ab
[2] => ac
[3] => ad
[4] => ae
[5] => af
[6] => ag
[7] => ah
[8] => ai
[9] => aj
[.... removed some values to save on length ....]
[1329] => 97
[1330] => 98
[1331] => 99
)
I have tried array_walk() and array_walk_recursive(), along with several foreach and while loops, to no avail.
I can get it to work by manually doing it for each length, but not with a variable length by doing this, but don't know how to make it variable by length.
function generate_two($l, $n, $d) {
$r = array();
foreach (generate_characters($l, $n, false) as $v1) {
foreach (generate_characters($l, $n, $d) as $v2) {
array_push($results, "$v1$v2");
}
}
return $r;
}
all this whilst, not having the '-' as the first character, although I could remove those values after generating the array if I needed to.
Thanks, Dan

Answer 1

Presuming you want to use the array you created as the array to use to append to. I can't see why you'd need to work with specific characters other than that in the array (I may be wrong, but this can be easily adapted to cater for that).
/**
* #param array $array
* #param $length
* #param null $original
* #return array
*/
function generate_values(array $array, $length, $original = null) {
// If length is 1 or less just return the array
if ($length <= 1) {
return $array;
}
// The resulting values array
$result = [];
// Copy the array if original doesn't exist
if (!is_array($original)) {
$original = $array;
}
// Loop over each item and append the original values
foreach($array as $item) {
foreach($original as $character) {
$result[] = $item . $character;
};
}
// Recursively generate values until the length is 1
return generate_values($result, --$length, $original);
}
To use it you can use your generator.
$characterArray = generate_characters(true, false, false);
$results = generate_values($characterArray, 2);

Answer 2

I don't know if this is the best solution but :
function generate_characters($length, $n, $d, $array = array()) {
$letters = array('a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','0','1','2','3','4','5','6','7','8','9');
$numbers = range(0, 9);
$others = array('-');
if($n == true)
$letters = array_merge($letters, $numbers);
if($d == true)
$letters = array_merge($letters, $others);
if(empty($array))
$array = $letters;
if(--$length <= 0)
return $array;
$result = array();
foreach ($array as $value) {
foreach ($letters as $add) {
$result[] = $value.$add;
}
}
return generate_characters($length, $n, $d, $result);
}
echo '<pre>';
print_r(generate_characters(3, true, true));

Answer 3

Sample code
function generate_characters($l, $n, $d)
{
// Start with an empty list
$r = array();
// Add the letters, if required
if ($l) {
$r = array_merge($r, range('a', 'z'));
}
// Add the digits, if required
if ($n) {
$r = array_merge($r, range('0', '9'));
}
// Add special characters, if required
if ($d) {
$r[] = '-';
}
return $r;
}
/**
* Generate all combinations of $len characters using the characters
* from a given list
*
* #param array $chars the list of characters to use
* #param int $len the length of strings to generate
* #return array
*/
function generate_combinations(array $chars, $len)
{
// $len <= 0: this is an error
// $len == 1: the input list is the output
if ($len <= 1) {
return $chars;
}
// Compute the output here
$result = array();
// Recursively compute the list of characters of length $len - 1
$partial = generate_combinations($chars, $len - 1);
// Append each entry from the input list to each string of length $len - 1 computed on the previous step
foreach ($partial as $head) {
foreach ($chars as $tail) {
// Put the combination in the output list
$result[] = $head.$tail;
}
}
// This is the list of all strings of length $len over the list $chars
return $result;
}
Usage
There is no need to call generate_characters() again and again. Given the same arguments, it always returns the same list of characters. Save it in a variable, use the variable further.
$chars = generate_characters(TRUE, FALSE, TRUE);
$comb2 = generate_combinations($chars, 2);
$comb5 = generate_combinations($chars, 5);
Remarks
While theoretically correct, generating all the combinations is completely useless in real life. The number of combinations increases exponentially and soon your script will use all the available memory to store the list.
I tested the code above and PHP 5.6 needed more than 2 GB of memory to generate all the combinations of 5 characters (using letters + dash). PHP 7 uses memory better and it required less than 1 GB of memory for the same task.
As you can imagine, it's impossible to use higher values for parameter $len; even for $len == 5, the amounts listed above are already huge.

Answer 4

If you want to combination of two array's value you can use directly this code. You does not required length of that array in your function.
function generateValue($array1, $array2) {
$result = array();
foreach ($array as $value) {
foreach ($original as $value2) {
$result[] = $value.$value2;
}
}
return $result;
}
print_r(generateValue($array1, $array2));