php query multidimensional array

PHP is a powerful programming language that is often used to develop web applications. When developing web applications through PHP, we often need to deal with multi-dimensional arrays. A multidimensional array is an array that contains another array. These arrays can be nested multiple levels into a complex structure. How to query such multi-dimensional arrays has become a problem faced by developers.

PHP provides some built-in functions to handle multi-dimensional arrays, including array_search(), array_key_exists(), in_array(), array_walk_recursive(), etc. This article will introduce several of these functions to help you easily query multi-dimensional arrays.

1. array_search() function

The array_search() function is used to find the specified element in the array and return its key name. If there are multiple matches in the array, the key name of the first match is returned. If there is no match, return false.

Here is the syntax of the array_search() function:

array_search(search_value, array, strict)

Where, search_value is the value to be found, array is the array to be searched , strict is an optional Boolean value used to specify whether type matching is required when searching. If set to true, the key names of elements with the same type and equal values ​​as search_value are returned. If set to false or not set, only the key names of elements with equal values ​​are returned.

The following is a sample code:

$students = [
    ['name' => '张三', 'age' => 20, 'gender' => '男'],
    ['name' => '李四', 'age' => 18, 'gender' => '女'],
    ['name' => '王五', 'age' => 22, 'gender' => '男']
];

// 查询名为'李四'的学生的索引
$index = array_search('李四', array_column($students, 'name'));
echo "李四的索引是：" . $index; 

In this example, we use the array_search() and array_column() functions. The array_column() function is used to return a new array containing the values ​​of the specified column. In this example, we return the name column of all students, then query the index of the element named '李思' in this array, and print it out.

2. array_key_exists() function

array_key_exists() function is used to determine whether a specified key name exists in the array. Returns true if present, false otherwise. The syntax of this function is as follows:

array_key_exists(key, array)

Among them, key is the key name to be found, and array is the array to be searched.

The following is a sample code:

$students = [
    '张三' => ['age' => 20, 'gender' => '男'],
    '李四' => ['age' => 18, 'gender' => '女'],
    '王五' => ['age' => 22, 'gender' => '男']
];

// 判断'李四'是否存在
if (array_key_exists('李四', $students)) {
    echo "存在名为'李四'的学生";
} else {
    echo "不存在名为'李四'的学生";
}

In this example, we use the array_key_exists() function to determine whether a key name exists in the array. If the entered key name '李思' exists in the array, it will return "There is a student named '李思'", otherwise it will return "There is no student named '李思'".

3. in_array() function

The in_array() function is used to determine whether a specified value exists in the array. Returns true if present, false otherwise. The syntax of this function is as follows:

in_array(needle, haystack, strict)

where needle is the value to be found, haystack is the array to search, and strict is an optional Boolean value , used to specify whether type matching is required when searching. If set to true, elements with the same type and equal values ​​as needle are returned. If set to false or not set, only elements with equal values ​​are returned.

The following is a sample code:

$fruits = ['apple', 'banana', 'orange'];

// 判断是否存在'banana'
if (in_array('banana', $fruits)) {
    echo "存在'banana'这个水果";
} else {
    echo "不存在'banana'这个水果";
}

In this example, we use the in_array() function to determine whether a value exists in the array. If the input value 'banana' exists in the array, it returns "the fruit 'banana' exists", otherwise it returns "the fruit 'banana' does not exist".

4. array_walk_recursive() function

array_walk_recursive() function is used to recursively traverse multi-dimensional arrays and execute the specified callback function. The syntax of this function is as follows:

array_walk_recursive(array, callback, userdata)

Among them, array is the multi-dimensional array to be traversed recursively, callback is the callback function to be executed, and userdata is passed to the callback Optional data for the function.

The following is a sample code:

$students = [
    ['name' => '张三', 'grades' => ['math' => 80, 'english' => 85]],
    ['name' => '李四', 'grades' => ['math' => 90, 'english' => 95]],
    ['name' => '王五', 'grades' => ['math' => 85, 'english' => 80]]
];

// 计算每个学生的平均分
function calculate_average(&$value, $key, $userdata) {
    $sum = array_sum($value['grades']);
    $value['average'] = round($sum / count($value['grades']), 2);
}

array_walk_recursive($students, 'calculate_average');

print_r($students); 

In this example, we use the array_walk_recursive() function to traverse a two-dimensional array containing multiple student names and grades, and calculate each student average score. In the callback function calculate_average(), we use the array_sum() function to calculate the total score of all subjects and divide it by the number of subjects to calculate the average score. Finally, we add the calculation results to each student's array and print the entire array using the print_r() function.

Summary

Querying multi-dimensional arrays is a common requirement in PHP development. This article introduces several built-in functions, including array_search(), array_key_exists(), in_array(), array_walk_recursive(), etc. These functions help us query and process multidimensional arrays easily. I hope readers gain something from this.

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