Filter arrays using PHP array_filter()

In PHP, the array_filter() function can help us quickly filter elements in an array. This article will introduce the usage of this function and related examples.

The basic syntax of the array_filter() function is:

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

Among them, the $array parameter is the array to be filtered, the $callback parameter is an optional callback function, and the $flag parameter is an optional Selected flag that determines how callback function return values ​​are handled.

Let’s explain these parameters one by one:

1. $array: The array to be filtered must be an array type.
2. $callback: optional callback function. If not specified, elements with a value of false will be automatically filtered out. The format of the callback function is function ($value), where $value is the value of the array element. If the callback function returns true, the element is retained, otherwise the element is removed.
3. $flag: used to specify how to handle the return value of the callback function. By default, the array_filter() function ignores elements with a return value of false, null, or an empty string. If the $flag parameter is specified as ARRAY_FILTER_USE_BOTH, the key name will be passed to the callback function.

Let’s take a look at some examples:

1. Filter out null values ​​and false values ​​​​in the array:

$array = array('foo', false, -1, null, '', 0);

$result = array_filter($array);

print_r($result);

Output results:

Array
(
    [0] => foo
    [2] => -1
)

2. Filter out the numbers less than 10 in the array:

$array = array(1, 20, 3, 40, 5, 60, 7, 80, 9);

$result = array_filter($array, function($value) {
    return $value > 10;
});

print_r($result);

Output result:

Array
(
    [1] => 20
    [3] => 40
    [5] => 60
    [7] => 80
)

3. Filter out all odd numbers in the array:

$array = array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

$result = array_filter($array, function($value) {
    return $value % 2 == 0;
});

print_r($result);

Output result:

Array
(
    [1] => 2
    [3] => 4
    [5] => 6
    [7] => 8
    [9] => 10
)

4. Keep the elements with even key names in the array:

$array = array(0 => 'foo', 1 => 'bar', 2 => 'baz', 3 => 'qux');

$result = array_filter($array, function($value, $key) {
    return $key % 2 == 0;
}, ARRAY_FILTER_USE_BOTH);

print_r($result);

Output result:

Array
(
    [0] => foo
    [2] => baz
)

To summarize, the array_filter() function is a very practical function that can help us quickly filter elements in the array and reduce the complexity and workload of the code. We can freely use callback functions to implement various filtering functions according to our own needs.

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