PHP array_unique() Function

Introduction to array_unique() in PHP

Duplicate values in an array can lead to incorrect results or inefficiencies in data processing. Removing the duplicates helps to maintain data integrity and efficiency. PHP offers a useful function called array_unique() that serves the purpose of removing duplicate values from an array. It takes an existing array as input and generates a new array that contains only the unique elements from the original one. This function proves to be especially beneficial when dealing with sizable datasets or arrays that are formed based on user input.

Syntax of array_unique() in PHP

The syntax of array_unique() is as follows:

Parameter Values of array_unique() in PHP

The array_unique() function accepts two parameters, as mentioned in the syntax. Let's take a closer look at each parameter:

• $array:
  This argument, which is required, identifies the array from which duplicate values are to be eliminated. An associative array, multidimensional array, or simply a straightforward indexed array can be used as the array.
• $flags (optional):
  The function's sorting behavior is controlled by the optional $flags parameter. It gives us a variety of sorting choices, including the ability to order elements as strings (SORT_STRING), numerically (SORT_NUMERIC), or in accordance with the current locale preferences (SORT_LOCALE_STRING). The sorting is done without changing types by default (SORT_REGULAR).

Return Value of array_unique() in PHP

The array_unique() function, as its name implies, returns an array that contains only the input array's unique members. Just the duplicate elements are removed, and the order of the elements is left as it was in the original array.

PHP Version

The PHP array_unique() method was introduced in PHP version 4.0.1. Since then, this function has been accessible, and all upcoming updates will continue to support it.

PHP Changelog

Examples of array_unique() in PHP

Remove Duplicate Values from An Array

Suppose we have an array $names that contains duplicate elements:

Output

Explanation

In this example, the array_unique() function will remove the duplicate names, and the resulting array $unique_names will contain only unique elements "Shubman", "Rohit", "Virat", and "Rishabh".

Working with Associative Arrays

The array_unique() function can also be used with associative arrays. Let's consider an example:

Output

Explanation

The use of the array_unique() function in this example ensures that the array $unique_students contains only unique elements by comparing their values. As a result, any duplicate associative arrays are removed, leaving behind only distinct elements.

Multidimensional Array

We can also handle multi-dimensional arrays using the array_unique() function. Let's take a look at an example:

Output

Explanation

The array_unique() function comes handy to remove duplicates in multidimensional arrays. When applied to the array, it diligently eliminates any duplicate sub-arrays, leaving us with a new version stored in the variable $unique_matrix. This updated array holds the unique arrays, without any duplicates cluttering our data.

Important Points about array_unique() in PHP

• The array_unique() function only removes duplicate values. It does not perform any sorting of the array elements.
• The function uses loose comparison (==) to determine the uniqueness of elements. This means that elements with different types but the same value will be considered duplicates.
• If the input array contains associative arrays, the function compares the elements using the SORT_REGULAR flag by default. It can be changed by specifying a different sorting flag as the second parameter.
• If the $array parameter is not an array, the array_unique() function will trigger a warning and return NULL.
• The function does not modify the original array. It returns a new array with unique elements.
• When using the SORT_NATURAL flag, the comparison of elements is performed in a human-friendly manner, taking into account numeric values within strings.
• If we want to remove duplicate elements while preserving the original keys, we can use the array_keys() function in combination with array_unique().

Limitation of array_unique() in PHP

• The array_unique() has a time complexity of O(n^2) in the worst case, where n is the number of elements of the array.
• The function creates a new array, potentially increasing memory consumption.
• The array_unique() does not support associative arrays.
• It performs loose comparisons, causing unexpected results with mixed string and integer values.
• It does not directly handle multidimensional arrays, custom logic is needed.
• Object comparison relies on the internal object representation, which may not recognize duplicates from different instances.