How does array_change_key_case() perform in large arrays?

M66 2025-04-25

In PHP, array_change_key_case() is a very common function, and its function is to convert all key names in an array to lowercase or uppercase. This function is very efficient for operating arrays with a small number of key-value pairs, but will performance become a bottleneck if the number of key-value pairs of the array is extremely large? Today we will discuss this issue.

1. Basic usage of array_change_key_case()

The syntax of array_change_key_case() is very simple:

 array_change_key_case(array $array, int $case = CASE_LOWER): array

$array : The array to be processed.
$case : Specifies whether to convert to lower case ( CASE_LOWER ) or upper case ( CASE_UPPER ). The default value is lowercase.

Example:

 $array = [
    "FIRST" => "apple",
    "SECOND" => "banana",
    "THIRD" => "cherry"
];

print_r(array_change_key_case($array, CASE_LOWER));

Output:

 Array
(
    [first] => apple
    [second] => banana
    [third] => cherry
)

2. Effect of array key number on performance

If we have tens of thousands or even more array keys to convert, can the performance of array_change_key_case() cope with such a large load? Let's analyze it.

Time complexity : The time complexity of array_change_key_case() is O(n), where n is the number of elements in the array. Because it requires iterating through each key and case conversion.
Space complexity : This function creates a new array, so the space complexity is O(n).

That is to say, when there are many keys in the array, the execution time of array_change_key_case() will be proportional to the memory occupied by the array size. For arrays that are tens of thousands or even larger, this can create some performance bottlenecks.

3. Performance testing

To verify the performance of array_change_key_case() when processing large amounts of data, we can write a simple test code.

 <?php
// Simulate a contains 10000 Array of keys
$array = [];
for ($i = 0; $i < 10000; $i++) {
    $array["KEY_" . $i] = "value" . $i;
}

// Time before the test
$start = microtime(true);
array_change_key_case($array, CASE_LOWER);
$end = microtime(true);

echo "Conversion time: " . ($end - $start) . " Second\n";
?>

Suppose we run the above code in a normal environment, the output time may be between a few hundred milliseconds and a second, depending on the performance of the server and the specific content of the array.

4. Performance optimization suggestions

If you need to do similar operations on large amounts of data frequently, here are some optimization suggestions:

Reduce call frequency : If possible, try to avoid frequent call to array_change_key_case() . For example, you can convert one at a time after the array is built, rather than every operation.
Manual Conversion : If you only need to convert certain keys, you can manually iterate over the array and convert specific keys, which avoids unnecessary overhead.

For example:

 foreach ($array as $key => $value) {
    $new_key = strtolower($key); // Custom conversion
    $new_array[$new_key] = $value;
}

This approach allows you to more precisely control which keys need to be converted, reducing unnecessary performance overhead.

5. Conclusion

array_change_key_case() is very efficient when dealing with small-scale arrays, but its performance may be affected if the size of the array reaches tens of thousands of elements. For large-scale data, optimization strategies are recommended, such as reducing call frequency or manually performing key conversions to avoid performance bottlenecks.

Of course, specific performance issues also need to be tested according to the actual environment. In development, it is often recommended to benchmark performance-sensitive parts to make more appropriate decisions.

array_change_key_case