PHP Sort Array by Key (With Examples)

Introduction

PHP is a flexible and robust programming language that provides an extensive set of functions and methods for efficient array manipulation. When working with arrays in PHP, it's important to understand that array keys can be of different types, such as strings or numbers. The array keys are used to identify and access specific elements within an array. While the sorting operation typically applies to the values in an array, PHP also provides functions to sort arrays by their keys.

Sorting an array by key means arranging the array elements based on their respective keys rather than their values. Sorting arrays by their keys allows for organizing data in a preferred sequence, facilitating the retrieval and analysis of information. In PHP, two essential functions, namely ksort() and krsort(), enable the sorting of associative arrays based on their keys.

Sorting Associative Arrays in Ascending Order

The ksort() function is specifically designed to sort associative arrays in ascending order based on their keys. It rearranges the elements of the array, preserving the key-value pairs, while ensuring that the keys are arranged in ascending order.

Syntax

Parameters

• $array:
  The array to be sorted. Note that the array is passed by reference.
• $sort_flags (optional):
  Specifies the mechanism for comparing array elements. The available values are:
  • 0 = SORT_REGULAR (default): Compares items normally without modifying their kinds.
  • 1 = SORT_NUMERIC: Compares items numerically.
  • 2 = SORT_STRING: Compares items as strings.
  • 3 = SORT_LOCALE_STRING: Uses the current locale to compare items as strings.
  • 4 = SORT_NATURAL: Uses natural sorting to compare items as strings.
  • 5 = SORT_FLAG_CASE: When used with SORT_STRING or SORT_NATURAL, it performs a case-insensitive comparison.

Return value

This function returns true on success or false on failure.

Example 1

Output

Explanation

In this example, we have an associative array $ages that stores the ages of various individuals, with the names serving as keys and the ages serving as values. The objective is to sort the array in ascending order using the keys.

The array's items are rearranged in-place using the ksort() method, which organizes the keys alphabetically. A foreach loop is then used to loop through the sorted array, printing each name and its related age. The names and ages are displayed in ascending order of the keys.

Example 2

Output

Explanation

In this example, we have an associative array named $products that contains product codes as keys and the names of the items as values. The goal is to sort the array in ascending order using the keys.

To do so, we can utilize the ksort() function, which allows us to reorganize the array items in-place. Based on the keys, this reordering is performed in an alphanumeric fashion. Following that, we use a foreach loop to traverse through the sorted array. We report each key-value combination to the console during the loop, displaying the product codes and their matching names in ascending order depending on the keys.

Sorting Associative Arrays in Descending Order

The krsort() function is similar to ksort() as it sorts associative arrays based on their keys. However, it differs in that krsort() arranges the keys in descending order, from highest to lowest.

Syntax

Parameters

• $array:
  The array to be sorted. Again, note that the array is passed by reference.
• $sort_flags (optional):
  Specifies the sorting behavior, just like in ksort(). Here also the default value is SORT_REGULAR.

Return value

Returns true on success or false on failure.

Example 1

Output

Explanation

In this example, the keys of the associative array $ages are the people's names, and the values are their ages. We want to rank the array descendingly based on the keys.

Using the krsort() function, the array is reorganized in-place, with the keys put in reverse alphabetical order. Each person's name and age are then printed using iteration in a foreach loop. The keys' names and ages are displayed in reverse chronological order in the output.

Example 2

Output

Explanation

The associative array $products in the example above has product codes as keys and their names as associated values. The array is to be sorted using the keys in decreasing order.

The array is changed in-place by rearranging the components such that the keys are listed in reverse alphabetical order using the krsort() method. The sorted array is then iterated through using a foreach loop, which echos each key-value pair. Based on the keys, the output lists the product codes and their matching names in decreasing order.

Use Case of Sorting Associative Arrays by Key

When displaying a list of items alphabetically, sorting an associative array by key can be helpful. Consider an array containing countries and their corresponding codes. Sorting the array by key allows us to present the countries in alphabetical order.

Example

Output

Explanation

In this example, the associative array gets sorted in ascending order according to the key of its elements.