PHP array key-value exchange: performance comparison and detailed explanation of the optimal solution

The best solution for PHP array key value exchange: use the built-in array_flip() function, the time complexity is O(n). For larger arrays, the performance advantages of array_flip() are more obvious. Practical case: array_flip() can be used to convert the array of product names in the shopping cart into an array of product quantities.

PHP array key-value exchange: performance comparison and detailed explanation of the optimal solution

In PHP, array is a useful data structure. Sometimes, you need to swap the keys and values ​​of an array to get a new array. This article compares three common methods and discusses their performance and best practices.

Method 1: Use the array_flip() function

$input = ['a' => 1, 'b' => 2, 'c' => 3];
$output = array_flip($input);

Method 2: Use the array_combine() function

$keys = array_keys($input);
$values = array_values($input);
$output = array_combine($values, $keys);

Method 3: Use a custom loop

$output = [];
foreach ($input as $key => $value) {
    $output[$value] = $key;
}

Performance comparison

Use array_flip( ) function is usually the fastest because it is a built-in function and is highly optimized. The array_combine() function is slightly slower because two extra function calls need to be performed (array_keys() and array_values()). The custom loop is the slowest because it requires manually looping through the entire array.

The following table summarizes the performance comparison of the three methods:

##array_combine()O(n * log( n))Custom loopO(n^2)

Method	Time complexity
array_flip()	O(n)

Best Practice

In most cases,

it is recommended to use the array_flip() function for key-value exchange. For smaller arrays, the performance difference is negligible. But for larger arrays, the advantages of the array_flip() function will become apparent.

Practical Case

Suppose we have an array of strings representing the names of the products in the shopping cart. To create another array where the keys are the product names and the values ​​are the product quantities, you can use the

array_flip() function:

$cart = ['Apple', 'Banana', 'Orange', 'Apple', 'Banana'];

// 创建商品数量数组
$counts = array_flip($cart);

The resulting array of

$counts It will look like this:

Array
(
    [Apple] => 2
    [Banana] => 2
    [Orange] => 1
)

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