Iterating Elements of Array without Loops

The examples are very abstract because there are cycles. Our condition will be as follows. It is necessary to select all elements of the array by a given attribute. Or, to put it more precisely, it is necessary to filter the array. There are several solutions.

The most suitable option in PHP is to use the built-in function array_filter(). Let’s imagine that it does not exist either. We write it using recursion.

On PHP, the function looks like this:

PHP

function getArrayElements($arr, $pattern) {
    static $i = 0;
    static $arrayResult = [];

    if (preg_match($pattern, $arr[$i])) {
        $arrayResult[] = $arr[$i];
    }

    $i++;

    if (count($arr) == $i) {
        return;
    } else {
        getArrayElements($arr, $pattern);
    }
    return $arrayResult;
}

Example:

PHP

$arr = ['a', 'xd', 'w', 1, 'y', 'x'];
$pattern = '/^x/';
print_r(getArrayElements($arr, $pattern)); // Array ( [0] => xd [1] => x )

Now let’s look at the same thing in JavaScript. In JS, an array has a similar filter() method. Let’s try to do without it, use recursion

JavaScript

let i = 0,
    arrayResult = [];
 
function getArrayElements(arr, pattern) {
    if (pattern.test(arr[i])) {
        arrayResult.push(arr[i]);
    }

    i++;

    if (arr.length == i) {
        return;
    } else {
        getArrayElements(arr, pattern);
    }
    return arrayResult;
}

Example:

JavaScript

const arr = ['a', 'xd', 'w', 1, 'y', 'x'],
      pattern = /^x/;

console.log(getArrayElements(arr, pattern)); //["xd", "x"]