What is the array_unique() method in PHP?

Overview

The array_unique() method will remove duplicate values from an array in PHP and is supported by PHP version 4 and later.

The array_unique() method will accept an array parameter whose duplicate will be removed from the array list and the filtered array returned. This duplicate will be removed using the flag, which was provided as the sorting method. If a duplicate is found in the array passed, it will be removed and one of it will be returned.

The keys of this array are not changed. When there are multiple elements, which are equal when compared, the key and value of the first equal element will be retained.

Note: We can only say that two values are equal if the elements being considered, that is (string) $firstElement === (string) $secondElement, have the same string form. If they are the same, then the first element will be used.

Syntax

array_unique($array_value,$flags)

Parameters

＄array_value: This is the array which we would want to remove duplicate values from, based on the flag provided.
＄flag: The second parameters ＄flag may be used to change the default sorting behavior of these values. The different options include the following.
- SORT_REGULAR: This compares items normally; that is, it won’t change types.
- SORT_NUMERIC: This compares items numerically.
- SORT_STRING: This compares items as strings.
- SORT_LOCALE_STRING: This compares items as strings, based on the current locale.

Return value

This returns an array with the duplicate values removed.

Code

Let’s take a look at the code example below.

<?php
//duplicate value home in the below array
$array_value = array("in" => "school", "market", "at" => "home", "party", "home");
$output1 = array_unique($array_value);
print_r($output1);
//duplicate id 1 in the array fruit
$fruits = array(
    1 => array("id"=>"3", "name"=>"apple",    "price"=>"2090"),
    1 => array("id"=>"4", "name"=>"mango", "price"=>"3493"),
    2 => array("id"=>"3", "name"=>"pineapple",  "price"=>"1390"),
    3 => "orange",
    3 => "orange",
);
$output2 = array_unique($fruits);
print_r($output2);
?>

Explanation

Line 4: We declare an array value with a duplicate.
Line 5: We use the array_unique method to remove the duplicate and save the output.
Line 6: We print the output array to display.
Lines 9–15: We contain all the members of the array ＄fruits, which has some duplicate elements. It is a nested array.
Line 17: We use the array_unique method to return unique contents of the variable ＄output2. The arrays with index key 1 were both removed, because even though they’re duplicates, their values are not ===, which is exactly the same as the strings. However, one of the duplicates of key index 3 was returned because the contained values are exactly the same.
Line 18: We print the resulting array.

License: Creative Commons-Attribution-ShareAlike 4.0 (CC-BY-SA 4.0)

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