Several methods for PHP to extract the value of a column of a two-dimensional array into a one-dimensional array

The extraction of a column from a two-dimensional array in PHP is a very common and frequently used function. Because of this, After PHP 5.5.0, a special function array_column() has been added. Of course, if your PHP version is lower than 5.5.0, you have to use other methods.

For example, for the following two-dimensional array:

We need to extract the usename column and change it into the following one-dimensional array:

The treatment methods are as follows:

1、 Array_column function method

array_column It is the simplest method, but the PHP version must be 5.5.0 and above. Method:

Output results:

Note: array_column(); The third parameter can be used to return the index/key column of the array. It can be the integer index of the column or the string key value. For example:

Output:

Note the ID difference between the two outputs above;

2、 Array_walk function method

array_walk() The function uses user-defined functions to callback each element in the array, and the method to realize the current function is as follows:

Note: "function() use() {}" is a way to write php closures. For details, see: How to use PHP Closure function() use() {} 。

3、 Array_map function method

array_map() The array_walk() function is similar to array_walk() in that it applies the callback function to the cell of a given array.

4、 Array_reduce function method

use array_reduce The method has a little more code, but the imagination space of this method (for other array value operations) is quite large:

Output:

The array_reduce method uses a callback function to iteratively operate on the value of the array, while create_function is used to call back an anonymous method. The parameter $result of this anonymous method is the value generated in the previous iteration, and $v is the current value. The internal implementation is to obtain the value of "username" of each item of the array $arr and push it to the new $result array;

5、 Foreach cycle method

foreach The loop is a little less efficient than the above method, but it is simple and easy to understand.

Note: My writing method is to directly foreach, and then array_push one by one into an array variable. This writing method may have a slight impact on performance, because using PHP native functions is certainly more efficient than looping.

6、 Array_map variant

The method is as follows, which means to remove the beginning value of each item value of the $wosn_net array, and obtain the removed value as a new array. Note that the key of the new array $username is still the key of the original array $wosn_net, as shown below.

The output is as follows:

Note: This function will obtain the id column in $wosn_net instead of the username column. The key of the output array is the key of the $wosn_net array, which coincides with no visible effect.

In addition, if you need to obtain the beginning or end columns of each item in the two-dimensional array, you can also do this:

These three variants have limited functions, and are only useful for obtaining the first or last column. They are difficult to work in complex arrays.

Reference link

https://www.awaimai.com/885.html

http://blog.it985.com/15036.html

http://blog.csdn.net/liruxing1715/article/details/22925575