How to remove duplicate elements from an array using PHP

PHP is a widely used server-side scripting language that can be used to quickly develop web applications. In PHP, array is a very important data type, which is often used to store and process complex data structures. During the development process, arrays often need to be manipulated and processed. One of the common requirements is to remove duplicate elements from the array. This article will introduce how to use PHP to remove duplicate elements from an array and provide corresponding example code.

1. Use the array_unique function to remove duplicate elements from the array

PHP’s built-in function array_unique can easily remove duplicate elements from the array. This function will retain the first element in the array and other duplicate elements will be deleted. The syntax of the array_unique function is as follows:

array array_unique ( array $array [, int $sort_flags = SORT_STRING ] )

Among them, $array represents the array that needs to be deduplicated, and $sort_flags represents the sorting method. , the default value is SORT_STRING.

The following is an example code for using the array_unique function to remove duplicate elements in an array:

<?php
$arr = array("apple","orange","banana","apple","banana");
$new_arr = array_unique($arr);
print_r($new_arr);
?>

The execution result of the above code is:

Array
(
    [0] => apple
    [1] => orange
    [2] => banana
)

2. Use the for loop and in_array function to remove the array Repeated elements in

In addition to using the array_unique function, we can also use a for loop to traverse the array and use the in_array function to determine whether the current element already exists in the array. If it does not exist, add the element to the new array. The following is an example code for using a for loop and the in_array function to remove duplicate elements from an array:

<?php
$arr = array("apple","orange","banana","apple","banana");
$new_arr = array();  // 定义一个新数组
foreach($arr as $value){
    if(!in_array($value,$new_arr)){  // 判断是否已经存在
        $new_arr[] = $value;  // 不存在则加入新数组
    }
}
print_r($new_arr);
?>

The execution result of the above code is the same as using the array_unique function:

Array
(
    [0] => apple
    [1] => orange
    [2] => banana
)

3. Use the array_flip function to remove elements from the array Repeated elements

Another way to remove duplicates is to use the array_flip function. This function will swap the keys and values ​​of the array, and duplicate keys will be removed. However, one thing to note with this method is that if the same value exists in the array, only the first value will be retained. The following is a sample code that uses the array_flip function to remove duplicate elements from an array:

<?php
$arr = array("apple","orange","banana","apple","banana");
$new_arr = array_flip($arr);
$new_arr = array_flip($new_arr);  // 还原数组
print_r($new_arr);
?>

The above code execution results are the same as the first two methods:

Array
(
    [apple] => 2
    [orange] => 1
    [banana] => 4
)

However, it should be noted that using the array_flip function to remove an array Repeated elements in will consume more time and system resources than using the first two methods.

4. Use the array_values ​​function to rebuild the array index

If we use the previous three methods to remove duplicate elements in the array, then the index of the new array will not be exactly the same as the original array, maybe There will be some problems with discontinuous indexes or key-value pair exchanges. In order to avoid this problem, we can use the array_values ​​function to rebuild the array index after deduplication. The following is a sample code:

<?php
$arr = array("apple","orange","banana","apple","banana");
$new_arr = array_unique($arr);
$new_arr = array_values($new_arr);
print_r($new_arr);
?>

The execution result of the above code is:

Array
(
    [0] => apple
    [1] => orange
    [2] => banana
)

After rebuilding the array index, the key values ​​of the new array will be exactly the same as the original array.

Summary:

This article introduces several PHP methods to remove duplicate elements from an array, including using the array_unique function, using the for loop and in_array function, and using the array_flip function. Choosing different methods according to the actual situation can improve the execution efficiency of the program and optimize the readability of the code. During the application process, you also need to pay attention to the index problem of the new array after deduplication. You can use the array_values ​​function to rebuild the index. I hope this article has provided some help and inspiration to readers in the processing of PHP arrays.

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