Using PHP's array_filter() Function to Filter Arrays

In PHP programming, arrays are a fundamental data type, and filtering array elements is a common operation; PHP provides the useful array_filter() function to accomplish this.

The array_filter() function applies a callback to each element of an array, keeping elements that satisfy the condition (callback returns true) and returns a new filtered array.

The function signature is:

array array_filter ( array $array [, callable $callback [, int $flag = 0 ]] )

Parameter description:

$array : the array to be filtered.

$callback : a user‑defined function that receives an element and returns a boolean; true keeps the element, false discards it. If omitted, the function removes elements that are falsey.

$flag : optional, determines how many arguments are passed to the callback. Default 0 passes only the value; a value greater than 0 also passes the key as the second argument.

Below are two examples demonstrating the use of array_filter():

Example 1: Filtering even numbers

<?php
// Original array
$arr = [1, 2, 3, 4, 5, 6];

// Filtering function
function filter_even($value) {
    return ($value % 2 == 0);
}

// Apply array_filter()
$new_arr = array_filter($arr, 'filter_even');

// Output result
print_r($new_arr);
?>

Running the code outputs:

Array
(
    [1] => 2
    [3] => 4
    [5] => 6
)

Example 2: Filtering empty values from an associative array

<?php
// Original array
$arr = [
    'name'   => 'Tom',
    'age'    => '',
    'gender' => 'male',
    'email'  => ''
];

// Filtering function
function filter_empty($value) {
    return ($value !== '');
}

// Apply array_filter()
$new_arr = array_filter($arr, 'filter_empty');

// Output result
print_r($new_arr);
?>

The output is:

Array
(
    [name]   => Tom
    [gender] => male
)

In summary, array_filter() is a versatile PHP function that simplifies array filtering by allowing custom callback logic, making it easy to implement a wide range of filtering scenarios in backend development.