Using PHP array_filter to Filter Arrays with Practical Examples

In PHP development, filtering arrays is a common task, and the built‑in array_filter function provides a flexible way to return a new array containing only elements that satisfy a given condition.

The basic syntax of array_filter is:

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

Parameters: $array: the array to be filtered. $callback (optional): a function that returns true for elements to keep. $flag (optional): controls how the callback receives arguments.

Below are three concrete examples demonstrating different uses of array_filter.

Example 1: Filter odd numbers from an array

$numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

$filteredNumbers = array_filter($numbers, function($value) {
    return $value % 2 == 1;
});

print_r($filteredNumbers);

Output:

Array
(
    [0] => 1
    [2] => 3
    [4] => 5
    [6] => 7
    [8] => 9
)

In this example, an anonymous function checks whether each element is odd.

Example 2: Filter strings longer than five characters

$names = ['John', 'Peter', 'Alice', 'David', 'Sarah'];

$filteredNames = array_filter($names, function($value) {
    return strlen($value) > 5;
});

print_r($filteredNames);

Output:

Array
(
    [2] => Alice
    [3] => David
)

Here the callback uses strlen to keep only strings whose length exceeds five.

Example 3: Use a class method as the callback

class Filter {
    public function isPositive($value) {
        return $value > 0;
    }
}

$numbers = [-1, 2, -3, 4, -5];
$filter = new Filter();

$filteredNumbers = array_filter($numbers, [$filter, 'isPositive']);

print_r($filteredNumbers);

Output:

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

This example defines a Filter class with an isPositive method and passes the method as a callback to array_filter.

In summary, array_filter is a powerful PHP function that can handle simple to complex filtering scenarios using anonymous functions or class methods as callbacks.