How to Use array_flip in PHP: Syntax and Examples

In PHP, array_flip swaps the keys and values of an array, turning values into keys and keys into values. Use it by passing your array to array_flip($array), which returns the flipped array.

Syntax

The array_flip function takes one parameter: the array you want to flip. It returns a new array where the original values become keys, and the original keys become values.

• array_flip(array $array): array
• $array: The input array to flip.

Note: Values in the original array must be valid keys (strings or integers). If values are duplicated, the last key will be used.

php

<?php
array_flip(array $array): array;
?>

Example

This example shows how array_flip swaps keys and values in a simple array.

php

<?php
$original = ['apple' => 'red', 'banana' => 'yellow', 'grape' => 'purple'];
$flipped = array_flip($original);
print_r($flipped);
?>

Output

Array
(
    [red] => apple
    [yellow] => banana
    [purple] => grape
)

Common Pitfalls

Common mistakes when using array_flip include:

• Using arrays with duplicate values: only the last key for a duplicated value is kept.
• Using values that are not strings or integers: these cannot become keys and will be ignored.
• Expecting the original array to be modified: array_flip returns a new array and does not change the original.

php

<?php
// Duplicate values example
$input = ['a' => 1, 'b' => 1, 'c' => 2];
$flipped = array_flip($input);
print_r($flipped);

// Output shows only last key for duplicate value 1
?>

Output

Array
(
    [1] => b
    [2] => c
)

Quick Reference

Function	Description
array_flip($array)	Returns a new array with keys and values swapped
Input values	Must be strings or integers to become keys
Duplicate values	Last key for duplicate value is used
Original array	Not modified by array_flip

Key Takeaways

Use array_flip to swap keys and values in an array easily.

Input values must be strings or integers to become valid keys.

If values repeat, only the last key is preserved in the flipped array.

array_flip returns a new array and does not change the original.

Check your array for duplicates to avoid unexpected results.