Master PHP’s array_flip: Swap Keys and Values with Easy Examples

PHP is a widely used server-side scripting language that provides powerful functions for handling arrays. One particularly useful function is array_flip(), which swaps the keys and values of an array.

Basic Syntax

array array_flip ( array $array )

The function accepts an array and returns a new array where the original keys become values and the original values become keys. If duplicate values exist, the last key is retained and earlier ones are discarded.

Simple Example

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

The output is:

Array
(
    [red] => apple
    [orange] => orange
    [yellow] => banana
)

Practical Use Case: Finding a Key by Value

When you need to locate a key based on its value, you can first flip the array and then use isset() to check for the desired value.

<?php
$students = array(
    "Tom"  => 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";
}
?>

The script outputs:

The student with age 20 is John

Conclusion

The array_flip() function is a powerful tool in PHP for swapping array keys and values, enabling efficient lookups, removal of duplicate values, and cleaner code in backend development.