How does PHP obtain a set of keys in a two-dimensional array (high-performance search)

Share the PHP method to obtain a set of keys in a two-dimensional array.

Specifically, for example, the next two-dimensional array is read from the database.

Code:

$ User = array (0 => array ('id' => 1, 'name' => 'zhang san', 'email '=> 'zhangsan @ sina.com ',), 1 => array ('id' => 2, 'name' => 'lily', 'email '=> 'lisi @ 163.com ',), 2 => array ('id' => 5, 'name' => 'wang wu ', 'email '=> '2017 @ qq.com ',),......);

The above array format is familiar with PHP + MYSQL.

Now there are two requirements:

1) obtain the index "id" set and save it as an array to obtain array (, 5)
If I used to write foreach directly, then array_push one by one into an array variable. This can also be achieved.
However, such writing affects performance, because using native PHP functions is certainly more efficient than looping.

Code:

$ids = array(); $ids = array_map('array_shift', $user);

The above code can get the desired result. For more information about function usage, see the manual.

In fact, there is also a solution to use the array_column function, but this function requires PHP version requirements (PHP 5> = 5.5.0)

Code:

$ids = array(); $ids = array_column($user, 'id');

In this case, the efficiency will certainly be higher.

2) obtain the set of index "name" and save it as an array to obtain the array ('zhang san', 'Li si', 'wang wu ')

According to my previous writing method, I still use the same foreach method. Then, array_push is pushed one by one to an array variable. Please refer to the efficient code.

Code:

$names = array(); $names = array_reduce($user, create_function('$v,$w', '$v[$w["id"]]=$w["name"];return $v;'));

Expected result:

Array (
1 => 'zhang san ',
2 => 'Li si ',
5 => 'wang wu ',
);