How to query the value of a multidimensional array in php

In the PHP development process, processing multi-dimensional arrays can greatly improve the flexibility and reusability of the code, because arrays can store large amounts of data. However, finding and manipulating data in multidimensional arrays can be confusing and overwhelming. Therefore, this article will introduce several common methods to query multi-dimensional array values.

1. Use loops

The simplest way to find values ​​in a multi-dimensional array is to loop the array and find the value we want by traversing the array.

Example: Suppose we have a multidimensional array about fruits, which contains the name, color and price of the fruits. We want to query the names of all fruits whose color is 'red'.

$fruits = array(
    'apple' => array(
        'color' => 'red',
        'price' => 1.00
    ),
    'banana' => array(
        'color' => 'yellow',
        'price' => 0.50
    ),
    'strawberry' => array(
        'color' => 'red',
        'price' => 2.00
    )
);

foreach ($fruits as $key => $value) {
    if ($value['color'] == 'red') {
        echo $key . '<br>'; // 输出：apple, strawberry
    }
}

In the above example, we iterate through the entire multidimensional array and check if the color in each sub-array is 'red'. If so, output the name of the fruit.

2. Use the array_map function

The array_map function is one of the built-in functions of the PHP language. It can apply a callback function to each element in the array and return the processed data.

Example: Suppose we want to query the names and email addresses of all users and store them in a new array.

$users = array(
    array(
        'name' => 'Tom',
        'email' => 'tom@example.com'
    ),
    array(
        'name' => 'Alice',
        'email' => 'alice@example.com'
    ),
    array(
        'name' => 'John',
        'email' => 'john@example.com'
    )
);

$result = array_map(function($item) {
    return array(
        'name' => $item['name'],
        'email' => $item['email']
    );
}, $users);

print_r($result);

In the above example, we use the array_map function to store each user's name and email address in a new array and return it.

3. Use the array_column function

The array_column function allows you to obtain a column of data in a multidimensional array and return a new array composed of the column of data.

Example: Suppose we have a multidimensional array of list of students containing their name, age and gender. We want to query the names of all students.

$students = array(
    array(
        'name' => 'Tom',
        'age' => 30,
        'gender' => 'male'
    ),
    array(
        'name' => 'Alice',
        'age' => 22,
        'gender' => 'female'
    ),
    array(
        'name' => 'John',
        'age' => 25,
        'gender' => 'male'
    )
);

$result = array_column($students, 'name');

print_r($result);

In the above example, we use the array_column function to get all the names in the student list and return a new array of them.

Conclusion

The above are several common methods of querying and operating multi-dimensional arrays. These methods provide a variety of options to obtain and process data in the array. Which method to choose depends on the specific application scenario and the programmer's personal style.

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