How to clear duplicate data from array in php

During the PHP development process, we often encounter situations where we need to clear duplicate data in arrays. If there are duplicate data in the array, it is likely to cause exceptions in the program and the results are not as expected, so it is very important to clear the duplicate data in the array. This article will introduce how to clear duplicate data from arrays in PHP.

1. Use the array_unique function

The array_unique function is a function that comes with PHP and can be used to remove duplicate data in the array. The syntax of the array_unique function is as follows:

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

Among them, $array is the array that needs to be cleared of duplicate data, and $sort_flags is an optional parameter used to control the behavior of the function.

For example:

<?php
$arr = array("PHP", "is", "the", "best", "programming", "language", "PHP");
$new_arr = array_unique($arr);
print_r($new_arr);
?>

The output of the above code is:

Array
(
    [0] => PHP
    [1] => is
    [2] => the
    [3] => best
    [4] => programming
    [5] => language
)

As you can see, the array_unique function successfully removes duplicate data in the array. It should be noted that the array_unique function uses the SORT_STRING method to sort the array by default. If you need to sort in other ways, you can use the $sort_flags parameter to set it.

It is worth mentioning that the array_unique function does not retain the key names in the original array when clearing the data, but only retains the value. If you need to preserve the key name, you can use the method described below.

2. Use the loop traversal method

In addition to using the array_unique function, you can also use the loop traversal method to clear duplicate data in the array. The specific operation is as follows:

<?php
$arr = array("PHP", "is", "the", "best", "programming", "language", "PHP");
$new_arr = array();
foreach($arr as $value) {
    if(!in_array($value, $new_arr)) {
        $new_arr[] = $value;
    }
}
print_r($new_arr);
?>

The output result of the above code is the same as the array_unique function, and the duplicate data in the array is also successfully cleared.

It should be noted that the loop traversal method is less efficient. When processing a large amount of data, it is recommended to use the array_unique function for clearing.

3. Use the array_keys and array_values ​​functions

If you need to retain the key names in the original array, you can use the array_keys and array_values ​​functions. The specific operation is as follows:

<?php
$arr = array("PHP", "is", "the", "best", "programming", "language", "PHP");
$arr = array_unique($arr);
$new_arr = array();
foreach($arr as $key => $value) {
    $new_arr[$key] = $value;
}
print_r($new_arr);
?>

The output result of the above code is still the array after removing duplicate data, but the key names in the original array are retained.

Summary

Clearing duplicate data in an array is a basic operation in PHP development. If not handled properly, it is likely to cause program exceptions and results that do not meet expectations. This article introduces several commonly used methods for removing duplicate data from arrays. You need to choose based on the actual situation when using them.

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