How to remove null values ​​from array in php

When developing PHP, we often need to process arrays. When processing arrays, we often need to remove null values ​​​​in the array to make the array cleaner and neater.

Null values ​​in the array do not affect the use of the array, but they will make the array look confusing and sometimes burden the program. Therefore, we need to process the array through PHP functions to remove null values.

PHP provides a variety of methods to remove null values ​​​​in an array, the most commonly used method is to use the function array_filter(). Below we will introduce in detail how to use this function.

1. Basic usage

The array_filter() function is a function in PHP used to filter unwanted values ​​​​in an array. The basic syntax of this function is as follows:

array array_filter (array $array [, callback $callback [, int $flag = 0 ]])

Among them, $array refers to the array to be filtered, $callback is an optional parameter, indicating the callback function to be applied (if not specified, all values ​​equal to false will be removed Elements). $flag is still an optional parameter. If set to PHP_ARRAY_FILTER_USE_BOTH, both the value and key will be checked to see if they are empty.

Look at an example below:

<?php
   $arr = array("a", "b", "", "c", "", "d");
   print_r(array_filter($arr));
?>

Output result:

Array
(
    [0] => a
    [1] => b
    [3] => c
    [5] => d
)

In the code here, we define an array $arr, which contains two empty elements." ”, after using the array_filter() function to filter out empty elements, only non-empty elements are retained, that is, [a, b, c, d].

2. Processing associative arrays

At the same time, we can also filter associative arrays. Filter functions are applied on values, so only key-value pairs that match the filter criteria are retained.

Look at an example below:

<?php
   $arr = array(
      "a" => 1,
      "b" => 2,
      "c" => "",
      "d" => 3,
      "e" => "",
      "f" => 4
   );
   print_r(array_filter($arr));
?>

Output result:

Array
(
    [a] => 1
    [b] => 2
    [d] => 3
    [f] => 4
)

Here we define an associative array $arr. We can see that after filtering, only Keys whose values ​​are not empty (a, b, d, f).

3. Use a custom callback function

If you want to customize filtering conditions, you can use a callback function to achieve it. The callback function receives the value of a single element in the array as a parameter and returns a Boolean value indicating whether the value should be retained.

Look at an example below:

<?php
   $arr = array("apple", "banana", "cherry", "donut", "elderberry");
   print_r(array_filter($arr, function($var) {
      return (strlen($var) > 4);
   }));
?>

Output result:

Array
(
    [2] => cherry
    [3] => donut
    [4] => elderberry
)

Here we define a callback function that determines whether to retain it based on the length of the element. Filter out elements whose length is less than or equal to 4, and the final output is [cherry, donut, elderberry].

4. For multi-dimensional arrays

The methods introduced above are all applicable to one-dimensional arrays. If you want to filter multi-dimensional arrays, how should you do it?

We can use a recursive function to process multi-dimensional arrays, as shown below:

<?php
   $arr = array(
      0 => 'some data',
      1 => '',
      2 => array(
         0 => 'more data',
         1 => '',
         2 => array(
            0 => 'even more data',
            1 => '',
         ),
      ),
   );
   function removeEmptyValues(&$array) {
      foreach($array as $key => &$value) {
         if(is_array($value)) {
            removeEmptyValues($value);
            if(count($value) == 0) {
               unset($array[$key]);
            }
         }
         else if(empty($value)) {
            unset($array[$key]);
         }
      }
      unset($value);
   }
   removeEmptyValues($arr);
   print_r($arr);
?>

Output results:

Array
(
    [0] => some data
    [2] => Array
        (
            [0] => more data
            [2] => Array
                (
                    [0] => even more data
                )
        )
)

Here, we define a recursive function removeEmptyValues() to Traverse the multi-dimensional array and process the elements inside, and null values ​​will be automatically eliminated.

Summary

Arrays are very common in PHP development, but sometimes the array may contain a large number of null values, occupying a large amount of storage space and affecting the performance of the program. In this case, we can use array_filter( ) function to remove null values ​​​​in the array, making the array cleaner and more efficient. It should be noted that when dealing with multi-dimensional arrays, we need to use recursive functions.

Of course, this is just a simple solution, and it does not apply to all situations. If you have a better method, please share it.

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