Combining array_map() and array_diff() to achieve conversion + comparison

In PHP, array_map() and array_diff() are two very commonly used array operation functions. array_map() is used to apply a callback function to each element in an array, while array_diff() is used to calculate the difference between two arrays. By combining these two functions, we can implement powerful data conversion and array comparison functions.

1. array_map() function

The array_map() function takes a callback function and one or more arrays as parameters and returns a new array where each element is the result of the callback function applying to the corresponding array elements.

grammar:

 array_map(callable $callback, array $array1, array $array2, ...);

2. array_diff() function

The array_diff() function is used to compare elements of two or more arrays and return elements that exist in the first array but not in other arrays.

grammar:

 array_diff(array $array1, array $array2, ...);

3. Application scenarios combining array_map() and array_diff()

Suppose we have two arrays: one is an array containing user personal information, and the other is an array of user records obtained from the database. We can use array_diff() to find out which user information does not exist in the database, and then use array_map() to convert or format this information.

The following is an example showing how to use these two functions to perform data conversion and array comparison.

Sample code:

 <?php
// Simulated user information array
$users = [
    ['id' => 1, 'name' => 'Zhang San', 'email' => 'zhangsan@example.com'],
    ['id' => 2, 'name' => 'Li Si', 'email' => 'lisi@example.com'],
    ['id' => 3, 'name' => 'Wang Wu', 'email' => 'wangwu@example.com']
];

// Simulated database record array（Assume that there are only the first two records in the database）
$dbUsers = [
    ['id' => 1, 'name' => 'Zhang San', 'email' => 'zhangsan@m66.net'],
    ['id' => 2, 'name' => 'Li Si', 'email' => 'lisi@m66.net']
];

// Get users that are not in the database record
$usersToAdd = array_diff(
    array_map(function($user) { return $user['email']; }, $users),
    array_map(function($user) { return $user['email']; }, $dbUsers)
);

// Output the user to be added
echo "Users that need to be added:\n";
foreach ($usersToAdd as $userEmail) {
    echo $userEmail . "\n";
}

?>

Code parsing:

1. Data preparation: We have two arrays $users and $dbUsers , where $users is the user data to be processed, and $dbUsers is the user record that already exists in the database.

2. Array comparison: Use array_map() to extract the email field of each element in the two arrays, and then use array_diff() to find out the email address in $users and which ones do not exist in $dbUsers .

3. Output result: Use foreach to loop to output the user email address you need to add.

4. Summary

By combining array_map() and array_diff() , we can implement very powerful data conversion and array comparison functions. This approach can help us quickly find out the differences between arrays and convert the results or process them further. In actual development, such techniques can help us efficiently process and clean data.