Master PHP’s array_flip(): Reverse Keys and Values with Confidence

Overview

The array_flip() function in PHP swaps the keys and values of an array, returning a new array with the inverted mapping. It is a frequently used utility for transforming associative arrays.

Syntax

array array_flip ( array $array )

Parameter

$array

– The input array whose keys and values you want to reverse.

Return Value

The function returns the flipped array. If the supplied argument is not a valid array, it returns bool(false).

Basic Example

$array = array(
    'a' => 'apple',
    'b' => 'banana',
    'c' => 'cherry'
);
$flippedArray = array_flip($array);
print_r($flippedArray);

Output:

Array
(
    [apple] => a
    [banana] => b
    [cherry] => c
)

Handling Duplicate Values

If the original array contains duplicate values, only the last key for each duplicated value is retained after flipping, because array keys must be unique.

$array = array(
    'a' => 'apple',
    'b' => 'banana',
    'c' => 'banana'
);
$flippedArray = array_flip($array);
print_r($flippedArray);

Output:

Array
(
    [apple] => a
    [banana] => c
)

Important Caveat

When using array_flip(), ensure that the original array’s values are unique and can be used as string keys; otherwise, later entries will overwrite earlier ones, leading to unexpected results.