Using PHP’s array_flip() Function to Swap Keys and Values

PHP is a widely used server‑side scripting language that provides powerful functions for handling arrays; one of them is array_flip() , which swaps the keys and values of an array.

The basic syntax is array array_flip ( array $array ) , which returns a new array where original keys become values and original values become keys. If duplicate values exist, the last key is kept.

Example 1 demonstrates flipping a fruit‑color associative array:

"red", "orange" => "orange", "banana" => "yellow");
$flipped_fruits = array_flip($fruits);
print_r($flipped_fruits);
?>

The output shows red => apple , orange => orange , and yellow => banana , confirming the key‑value exchange.

Example 2 shows a practical lookup scenario: after flipping a student‑age array, isset() can be used to find a name by age.

18, "John" => 20, "Mary" => 19);
$flipped_students = array_flip($students);
$age_to_find = 20;
if (isset($flipped_students[$age_to_find])) {
    $student_name = $flipped_students[$age_to_find];
    echo "The student with age $age_to_find is $student_name";
} else {
    echo "No student with age $age_to_find";
}
?>

This script outputs “The student with age 20 is John”, illustrating how array_flip() enables reverse lookups.

In real development, array_flip() is useful for tasks such as searching for keys by value, removing duplicate values, and simplifying code, thereby improving efficiency and readability.

In summary, mastering array_flip() helps PHP developers handle associative arrays more effectively.