Using array_filter() to Filter Arrays in PHP

In PHP programming, arrays are a common data type, and filtering array elements is a frequent operation. PHP provides the useful array_filter() function for this purpose.

The array_filter() function applies a callback to filter an array, keeping elements that satisfy the condition and returning a new array.

Usage syntax:

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

Parameters:

$array: the array to be filtered.

$callback: a callable that receives each element and returns a boolean; true keeps the element, false discards it. If omitted, elements evaluating to false are removed.

$flag (optional): determines how many arguments are passed to the callback. Default 0 passes only the value; a value >0 passes both value and key.

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

Example One: Filtering Even Numbers

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

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

// Use 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 Two: 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 !== '');
}

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

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

Running the code outputs:

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

These examples show two scenarios of using array_filter() to filter array elements. In real development, the function has many other applications, and developers can apply it flexibly according to their needs.

Summary

The array_filter() function is a widely used and practical tool in PHP that provides a convenient way to filter array elements. By using a callback to test each element, developers can implement various flexible filtering requirements, deepening their understanding of array handling in backend development.