The array_unique() function in PHP is used to remove duplicate values from an array. This function compares the values in the array and returns a new array containing only the unique values. It is particularly useful when you want to ensure that your array contains distinct elements, eliminating redundancy.

Syntax:

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

Parameters:

• $array: The input array from which to remove duplicate values.
• $sort_flags: (Optional) A flag that can be used to specify how the values should be compared. The default is SORT_STRING, which treats values as strings. Other options include:
  • SORT_REGULAR: Compare items normally (default behavior).
  • SORT_NUMERIC: Compare items numerically.
  • SORT_STRING: Compare items as strings.
  • SORT_LOCALE_STRING: Compare items as strings, based on the current locale.

Return Value:

• Returns a new array containing unique values from the input array. The keys of the original array are preserved.

Example 1: Basic Usage

In this example, we demonstrate how to use array_unique() to remove duplicate values.

<?php
$array = [1, 2, 2, 3, 4, 4, 5];
$uniqueArray = array_unique($array);

print_r($uniqueArray);
?>

Output:

Array
(
    [0] => 1
    [1] => 2
    [3] => 3
    [4] => 4
    [6] => 5
)

In this case, the duplicate values 2 and 4 are removed, leaving the unique elements.

Example 2: Preserving Keys

The keys of the original array are preserved in the new array.

<?php
$array = [0 => 'apple', 1 => 'banana', 2 => 'apple', 3 => 'orange'];
$uniqueArray = array_unique($array);

print_r($uniqueArray);
?>

Output:

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

Here, the key 2 associated with the second occurrence of 'apple' is not included in the result, but the keys of other unique values are preserved.

Example 3: Working with Strings

You can also use array_unique() with arrays of strings.

<?php
$array = ['a', 'b', 'b', 'c', 'a'];
$uniqueArray = array_unique($array);

print_r($uniqueArray);
?>

Output:

Array
(
    [0] => a
    [1] => b
    [3] => c
)

In this example, the duplicate string values are removed, resulting in an array of unique strings.

Example 4: Using Sort Flags

You can specify a sort flag to compare values in a specific way. For example, using SORT_NUMERIC can be useful when you have numeric strings.

<?php
$array = ['1', '1.0', 1, 2, '2'];
$uniqueArray = array_unique($array, SORT_NUMERIC);

print_r($uniqueArray);
?>

Output:

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

Here, the string '1' and the integer 1 are considered equal when compared numerically, so only one instance is kept.

Practical Usage:

• array_unique() is useful for:
  • Cleaning up data by removing duplicates.
  • Ensuring that lists of items (such as product IDs, names, etc.) contain only distinct entries.
  • Preparing data for further processing or analysis.

Summary:

• array_unique($array, $sort_flags) removes duplicate values from an array and returns a new array containing only unique values.
• The keys from the original array are preserved in the new array.
• This function is a simple and effective way to handle duplicates in arrays in PHP.