Summary of methods for converting PHP two-dimensional array (or any dimensional array) into one-dimensional array

Suppose there is the following two-dimensional array:

$user = array(
    '0' => array('id' => 100, 'username' => 'a1'),
    '1' => array('id' => 101, 'username' => 'a2'),
    '2' => array('id' => 102, 'username' => 'a3'),
    '3' => array('id' => 103, 'username' => 'a4'),
    '4' => array('id' => 104, 'username' => 'a5'),
);

Now we want to convert it into a one-dimensional array, there are two situations:

One It converts the specified column into a one-dimensional array, which is summarized in another article: "Comprehensive method of extracting a specified column from a multi-dimensional array in PHP".

Now we focus on the second case, which is to convert all values ​​into a one-dimensional array, and the key values ​​​​are the same and will not be overwritten. The converted one-dimensional array looks like this:

$result = array(100, 'a1'， 101, 'a2', 102, 'a3', 103, 'a4', 104, 'a5');

There are mainly the following methods.

1 array_reduce function method

Using the array_reduce() function is a faster method:

$result = array_reduce($user, function ($result, $value) {
    return array_merge($result, array_values($value));
}, array())

Because the array_merge function will merge the same characters Arrays of string key names are overwritten and merged, so the values ​​must be retrieved using array_value before merging.

If the second dimension is a numeric key name, such as:

$user = array(
    'a' => array(100, 'a1'),
    'b' => array(101, 'a2'),
    'c' => array(102, 'a3'),
    'd' => array(103, 'a4'),
    'e' => array(104, 'a5'),
);

, then just do this:

$result = array_reduce($user, 'array_merge', array())

2 array_walk_recursive function method

The array_walk_recursive() function is very flexible and can convert an array of any dimension into a one-dimensional array.

$result = [];
array_walk_recursive($user, function($value) use (&$result) {
    array_push($result, $value);
});

For example, the following multi-dimensional array:

$user4 = array(
    'a' => array(100, 'a1'),
    'b' => array(101, 'a2'),
    'c' => array(
        'd' => array(102, 'a3'),
        'e' => array(103, 'a4'),
    ),
);

After using this method, it becomes:

$result = array(100, 'a1'， 101, 'a2', 102, 'a3', 103, 'a4');

3 array_map function method

The methods of using array_map and array_reduce functions are similar, as follows:

$result = [];
array_map(function ($value) use (&$result) {
    $result = array_merge($result, array_values($value));
}, $user);

Just need to declare an empty $result array.

In addition, you can also use the array_walk method and the foreach loop method. The principles are the same as above.

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