Introduction to PHP functions—array_filter(): Use callback functions to filter elements in an array

PHP function introduction—array_filter(): Use callback function to filter elements in the array

In PHP programming, array is a very common and important data type. As for array operations, one of the most common operations is to filter elements in the array. PHP provides a very practical function array_filter() to achieve this function.

The array_filter() function is to use the callback function to filter the array, retain the elements in the array that meet the conditions, and return a new array.

The array_filter() function is used as follows:

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

Parameter description:

• $array: the array to be filtered;
• $callback : Callback function, used to test elements in the array. This function accepts a parameter, representing the element in the array, and returns a Boolean value in the callback function. If it returns true, the element will be retained, and if it returns false, the element will be filtered. If the callback function is not provided, elements with a value of false are filtered out by default;
• $flag: optional parameter, which specifies the number of parameters passed in the callback function. The default is 0, which means the callback function only accepts one parameter (an element in the array). If a value greater than 1 is passed, the callback function accepts two parameters, the first parameter is the element in the array, and the second parameter is the key of the element.

Below we use several examples to demonstrate the use of the array_filter() function.

Example 1: Filter even numbers in the array

<?php
// 原始数组
$arr = [1, 2, 3, 4, 5, 6];

// 过滤函数
function filter_even($value) {
    return ($value % 2 == 0);
}

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

// 输出结果
print_r($new_arr);
?>

Run the above code, the output result is:

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

Example 2: Filter empty values ​​in the associative array

<?php
// 原始数组
$arr = ['name' => 'Tom', 'age' => '', 'gender' => 'male', 'email' => ''];

// 过滤函数
function filter_empty($value) {
    return ($value !== '');
}

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

// 输出结果
print_r($new_arr);
?>

Run the above code, the output result is:

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

The above two examples respectively show two cases of using the array_filter() function to filter elements in the array. In actual development, the array_filter() function has many other application scenarios, which we can use flexibly according to actual needs.

Summary:
The array_filter() function is a very commonly used and practical function in PHP. It provides a convenient way to filter elements in an array. By using callback functions to determine whether array elements meet conditions, we can implement various flexible filtering requirements. I hope the introduction in this article can help everyone and give everyone a deeper understanding of the use of the array_filter() function.

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