Using PHP’s array_unique() Function to Remove Duplicate Array Elements

In PHP programming, array manipulation is common. The built‑in array_unique() function removes duplicate values from an array and returns a new array.

Syntax of array_unique()

array_unique(array $array, int $sort_flag = SORT_STRING): array

Parameter explanation

$array

: the input array to be deduplicated. $sort_flag: optional flag that determines how the array elements are sorted during deduplication.

Return value: an array containing only the first occurrence of each value.

Usage of array_unique()

<?php
// Define an array with duplicate elements
$fruits = array("apple", "banana", "orange", "apple", "melon", "banana");

// Remove duplicates
$uniqueFruits = array_unique($fruits);

// Output the result
print_r($uniqueFruits);
?>

The code defines $fruits, calls array_unique() to produce $uniqueFruits, and prints the deduplicated array.

Running the script yields:

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

As shown, the duplicate entries “apple” and “banana” appear only once, while the other elements remain unchanged.

The optional $sort_flag argument can be set to control the sorting behavior. Two common values are: SORT_STRING (default): treats elements as strings and sorts them lexicographically. SORT_REGULAR: compares elements using regular PHP comparison rules.

Example with $sort_flag

<?php
$numbers = array(1, 3, 5, 2, 5, 4);

// Remove duplicates and sort as strings
$uniqueNumbers = array_unique($numbers, SORT_STRING);

// Output the result
print_r($uniqueNumbers);
?>

The output is:

Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [4] => 4
    [5] => 5
)

By specifying $sort_flag = SORT_STRING, the numeric values are treated as strings, sorted in dictionary order, and the resulting array is ordered ascending.

The array_unique() function is a convenient tool in PHP for quickly removing duplicate elements from arrays. Using the optional $sort_flag parameter, developers can also control the sorting method, simplifying array handling and improving code efficiency.

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