How to Print Unique Elements an Given Array in PHP?

Given an array, the task is to print all distinct elements of the given array. The given array may contain duplicates and the output should print every element only once. The given array is not sorted.

Examples:

Input: arr[] = {5, 6, 5, 3, 6, 4, 3, 5}
Output: 5, 6, 3, 4
Input: arr[] = {1, 2, 3, 4, 5, 5, 4, 3, 3, 3}
Output: 1, 2, 3, 4, 5

There are two methods to solve this problem, these are:

Using array_unique() Function

The array_unique() function is used to remove the duplicate values from an array. If there are multiple elements in the array with same values then the first appearing element will be kept and all other occurrences of this element will be removed from the array.

Syntax:

array array_unique($array , $sort_flags)

Example:

<?php

$array = [1, 1, 3, 3, 3, 4, 4, 5, 7];

$printUniqueElements = array_unique($array);

print_r($printUniqueElements);

?>

Array
(
    [0] => 1
    [2] => 3
    [5] => 4
    [7] => 5
    [8] => 7
)

Using Nested Loop

We can print unique elements using nested loop. The outer loop picks an element one by one starting from the leftmost element. The inner loop checks if the element is present on left side of it. If present, then ignores the element, else prints the element.

Example:

<?php

function printUniqueElements($arr, $len) {

    for($i = 0; $i < $len; $i++) {
        $j = 0; 
        for($j; $j < $i; $j++) {
            if ($arr[$i] == $arr[$j])
                break;
        }
        if ($i == $j)
            echo $arr[$i] , " ";
    }
}
   
// Driver function
$arr = [12, 10, 9, 45, 2, 10, 10, 45];
$len = sizeof($arr);

printUniqueElements($arr, $len);

?>

12 10 9 45 2 

Using a Hash Table

A hash table (or dictionary in some languages) allows for efficient insertion and lookup operations. By leveraging a hash table, we can ensure each element is processed in constant time, making the approach both time-efficient and straightforward.

Example:

<?php

function printUniqueElements($arr) {
    $seen = array(); // Hash table to keep track of seen elements

    foreach ($arr as $value) {
        if (!in_array($value, $seen)) {
            echo $value . " ";
            $seen[] = $value;
        }
    }
}

// Driver function
$arr = [12, 10, 9, 45, 2, 10, 10, 45];
printUniqueElements($arr);

?>

12 10 9 45 2