Detailed explanation of the usage of PHP's array_column() function

In PHP, it is often necessary to process and operate arrays. Sometimes, you need to obtain a specific column of data from a multi-dimensional array. In this case, you can use the array_column() function to achieve this. This article will introduce the usage of array_column() function in detail.

1. What is the array_column() function

array_column() is a PHP function used to obtain a specified column of data from a multi-dimensional array. This function was introduced in PHP 5.5 and supports associative arrays and indexed arrays.

Function prototype:
array_column ( array $array , mixed $column_key [, mixed $index_key = null ] ) : array

Parameter description:
$array: to be operated Multidimensional array;
$column_key: the key name or value of the column to be obtained;
$index_key: optional parameter, if this value is specified, it will be used as the key name of the returned array.

2. Usage Examples

Let’s look at some usage examples of the array_column() function.

1. Index array

Suppose we have an index array $users, which stores some user information, and we want to get the names of all users from it. This can be achieved through the following code:

$users = array(0 => array('id'=>1, 'name'=>'Tom', 'email'=>'tom@example.com'),
               1 => array('id'=>2, 'name'=>'Jerry', 'email'=>'jerry@example.com'),
               2 => array('id'=>3, 'name'=>'Mike', 'email'=>'mike@example.com'));

$names = array_column($users, 'name');

print_r($names);

The output result is:

Array (
    [0] => Tom
    [1] => Jerry
    [2] => Mike
)

2. Associative array

If our array is an associative array, we can Get a specified column of data in the same way.

For example, we have an associative array $students, which contains some information about students. We want to get the ages of all students:

$students = array('Tom' => array('age'=>20, 'gender'=>'male', 'city'=>'Beijing'),
                  'Jerry' => array('age'=>21, 'gender'=>'female', 'city'=>'Shanghai'),
                  'Mike' => array('age'=>19, 'gender'=>'male', 'city'=>'Guangzhou'));

$ages = array_column($students, 'age');

print_r($ages);

The output result is:

Array (
    [Tom] => 20
    [Jerry] => 21
    [Mike] => 19
)

3. Get multiple key values

If we want to get multiple key values ​​from a multi-dimensional array, we can put the key names to be obtained in an array and pass them as the second parameter Enter the array_column() function.

For example, we have an array $temperatures that contains temperature data for multiple cities. We want to get the average temperature and maximum temperature of each city. We can do this:

$temperatures = array(
    array('city'=>'Beijing', 'average'=>20, 'highest'=>28),
    array('city'=>'Shanghai', 'average'=>23, 'highest'=>30),
    array('city'=>'Guangzhou', 'average'=>25, 'highest'=>32)
);

$infos = array_column($temperatures, array('average', 'highest'), 'city');

print_r($infos);

Output results Specify the key name of the returned array for:

Array (
    [Beijing] => Array (
        [average] => 20
        [highest] => 28
    )
    [Shanghai] => Array (
        [average] => 23
        [highest] => 30
    )
    [Guangzhou] => Array (
        [average] => 25
        [highest] => 32
    )
)

Sometimes, we want to specify the key name of the returned array when obtaining the data of the specified column. Can be specified in the third parameter of the array_column() function.

For example, in the previous example, we hope to use "average temperature" and "maximum temperature" as the key names of the returned array. We can write like this:

$temperatures = array(
    array('city'=>'Beijing', 'average'=>20, 'highest'=>28),
    array('city'=>'Shanghai', 'average'=>23, 'highest'=>30),
    array('city'=>'Guangzhou', 'average'=>25, 'highest'=>32)
);

$infos = array_column($temperatures, array('average', 'highest'), 'city');

$infos = array_map(function($v){return ['平均气温'=>$v[0], '最高气温'=>$v[1]];}, $infos);

print_r($infos);

The output result is:

Array (
    [Beijing] => Array (
        [平均气温] => 20
        [最高气温] => 28
    )
    [Shanghai] => Array (
        [平均气温] => 23
        [最高气温] => 30
    )
    [Guangzhou] => Array (
        [平均气温] => 25
        [最高气温] => 32
    )
)

3. Conclusion

The array_column() function can easily obtain a specified column of data from a multi-dimensional array, and the method of use is simple and clear. In actual development, we can make full use of this function to improve the efficiency and accuracy of array processing.

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