Sorting an associative array by key is a common task in PHP, especially when you need to organize data alphabetically or numerically based on keys. PHP provides built-in functions to accomplish this task efficiently, allowing developers to rearrange the order of elements within an associative array based on their keys.

Approach:

• Using ksort() Function: The ksort() function is specifically designed to sort an associative array by its keys in ascending order. It rearranges the elements of the array based on their keys while maintaining key-value associations.
• Using krsort() Function: The krsort() function sorts an associative array by its keys in descending order. It rearranges the elements of the array in reverse order based on their keys while preserving key-value associations.

Syntax:

// Using ksort() function (ascending order)
ksort($array);
// Using krsort() function (descending order)
krsort($array);

Example: Implementation to sort an associative array by key.

Array
(
    [a] => 1
    [b] => 2
     => 3
)
Array
(
     => 3
    [b] => 2
    [a] => 1
)

Difference between ksort() and krsort() Methods