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 keep elements that satisfy a given condition.

The function signature is:

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

where $array is the input array, $callback is an optional function that returns true for elements to keep, and $flag controls callback behavior.

Example 1 shows how to filter odd numbers from an integer array using an anonymous function:

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

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

print_r($filteredNumbers);

The output is:

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

Example 2 filters strings longer than five characters from an array of names, using strlen inside the callback:

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

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

print_r($filteredNames);

The resulting array contains:

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

Example 3 demonstrates using a class method as the callback. A Filter class defines an isPositive method, and an instance is passed to array_filter:

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);

The output shows the positive numbers:

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

In summary, array_filter is a powerful PHP function that simplifies array filtering; complex conditions can be handled with anonymous functions or class methods, making it a valuable tool for backend developers.