Using PHP array_flip() Function: Syntax, Examples, and Practical Applications

PHP's array_flip() function swaps the keys and values of an array, turning original keys into values and vice versa. Its syntax is array array_flip ( array $array ) , and it returns a new array with the exchanged pairs.

Example usage shows an associative array $old_array = array("apple"=>"fruit", "carrot"=>"vegetable"); being flipped with $new_array = array_flip($old_array); and displayed using var_dump($new_array); , producing a result where "fruit" and "vegetable" become keys.

<code>$old_array = array("apple"=>"fruit", "carrot"=>"vegetable");
$new_array = array_flip($old_array);
var_dump($new_array);
</code>

One practical application is removing duplicate values: an indexed array is flipped, unique keys are kept with array_unique() , and then flipped back, yielding an array without duplicates.

<code>$old_array = array("apple", "banana", "carrot", "apple", "grape", "banana");
$new_array = array_flip($old_array);
$new_array = array_unique($new_array);
$new_array = array_flip($new_array);
print_r($new_array);
</code>

Another use case is quickly locating a value's original key by flipping the array and checking existence with isset() or array_key_exists() .

<code>$old_array = array("apple"=>"fruit", "banana"=>"fruit", "carrot"=>"vegetable");
$new_array = array_flip($old_array);
if (isset($new_array["fruit"])) {
    echo "fruit is found in array";
}
</code>

For generating enumerated arrays, array_flip() can turn a list of values into keys, which are then paired with sequential numbers using range() and array_map() , finally merging with array_replace() to produce an array mapping each item to an index.

<code>$old_array = array("Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday");
$new_array = array_flip($old_array);
$enum_array = array_map(function(){static $index = 1; return $index++;}, range(1, count($old_array)));
$new_array = array_replace($new_array, $enum_array);
print_r($new_array);
</code>

The article concludes with several recommended learning resources for PHP and related technologies, linking to tutorials on Vue3, Laravel, Swoole, and Workerman.