PHP array_filter with arguments

I have the following code:

function lower_than_10($i) {
    return ($i < 10);
}

that I can use to filter an array like this:

$arr = array(7, 8, 9, 10, 11, 12, 13);
$new_arr = array_filter($arr, 'lower_than_10');

How can I add arguments to lower_than_10 so that it also accepts the number to check against? Like, if I have this:

function lower_than($i, $num) {
    return ($i < $num);
}

how to call it from array_filter passing 10 to $num or whatever number?

if you are using php 5.3 and above, you can use closure to simplify your code:

$NUM = 5;
$items = array(1, 4, 5, 8, 0, 6);
$filteredItems = array_filter($items, function($elem) use($NUM){
    return $elem < $NUM;
});

As an alternative to @Charles's solution using closures, you can actually find an example in the comments on the documentation page. The idea is that you create an object with the desired state ($num) and the callback method (taking $i as an argument):

class LowerThanFilter {
        private $num;
 
        function __construct($num) {
                $this->num = $num;
        }
 
        function isLower($i) {
                return $i < $this->num;
        }
}

Usage (demo):

$arr = array(7, 8, 9, 10, 11, 12, 13);
$matches = array_filter($arr, array(new LowerThanFilter(12), 'isLower'));
print_r($matches);

---

As a sidenote, you can now replace LowerThanFilter with a more generic NumericComparisonFilter with methods like isLower, isGreater, isEqual etc. Just a thought — and a demo...

In PHP 5.3 or better, you can use a closure:

function create_lower_than($number = 10) {
// The "use" here binds $number to the function at declare time.
// This means that whenever $number appears inside the anonymous
// function, it will have the value it had when the anonymous
// function was declared.
    return function($test) use($number) { return $test < $number; };
}

// We created this with a ten by default.  Let's test.
$lt_10 = create_lower_than();
var_dump($lt_10(9)); // True
var_dump($lt_10(10)); // False
var_dump($lt_10(11)); // False

// Let's try a specific value.
$lt_15 = create_lower_than(15);
var_dump($lt_15(13)); // True
var_dump($lt_15(14)); // True
var_dump($lt_15(15)); // False
var_dump($lt_15(16)); // False

// The creation of the less-than-15 hasn't disrupted our less-than-10:
var_dump($lt_10(9)); // Still true
var_dump($lt_10(10)); // Still false
var_dump($lt_10(11)); // Still false

// We can simply pass the anonymous function anywhere that a
// 'callback' PHP type is expected, such as in array_filter:
$arr = array(7, 8, 9, 10, 11, 12, 13);
$new_arr = array_filter($arr, $lt_10);
print_r($new_arr);

if you need multiple parameters to be passed to the function, you may append them to the use statement using ",":

$r = array_filter($anArray, function($anElement) use ($a, $b, $c){
    //function body where you may use $anElement, $a, $b and $c
});

In extension to jensgram answer you can add some more magic by using the __invoke() magic method.

class LowerThanFilter {
    private $num;

    public function __construct($num) {
        $this->num = $num;
    }

    public function isLower($i) {
        return $i < $this->num;
    }

    function __invoke($i) {
        return $this->isLower($i);
    }
}

This will allow you to do

$arr = array(7, 8, 9, 10, 11, 12, 13);
$matches = array_filter($arr, new LowerThanFilter(12));
print_r($matches);

class ArraySearcher{

const OPERATOR_EQUALS = '==';
const OPERATOR_GREATERTHAN = '>';
const OPERATOR_LOWERTHAN = '<';	
const OPERATOR_NOT = '!=';		

private $_field;
private $_operation;
private $_val;

public function __construct($field,$operation,$num) {
	$this->_field = $field;
	$this->_operation = $operation;
    $this->_val = $num;
}


function __invoke($i) {
	switch($this->_operation){
    	case '==':
			return $i[$this->_field] == $this->_val;
		break;
		
		case '>':
			return $i[$this->_field] > $this->_val;
		break;
		
		case '<':
			return $i[$this->_field] < $this->_val;
		break;
		
		case '!=':
			return $i[$this->_field] != $this->_val;
		break;
	}
}


}

This allows you to filter items in multidimensional arrays:

$users = array();
$users[] = array('email' => '[email protected]','name' => 'Robert');
$users[] = array('email' => '[email protected]','name' => 'Carl');
$users[] = array('email' => '[email protected]','name' => 'Robert');

//Print all users called 'Robert'
print_r( array_filter($users, new ArraySearcher('name',ArraySearcher::OPERATOR_EQUALS,'Robert')) );

Worth noting that since PHP 7.4 arrow functions are available, and this can be done even more neatly:

$max = 10;
$arr = array(7, 8, 9, 10, 11, 12, 13);
$new_arr = array_filter($arr, fn ($n) => $n < $max);