Master PHP’s array_flip(): Swap Keys and Values with Ease

In PHP programming, arrays are a fundamental data structure, and the array_flip() function provides a convenient way to exchange an array's keys and values.

Function Purpose

The function takes an input array and returns a new array where each original value becomes a key and each original key becomes a value. If a value is not a string or integer, the function triggers an error.

Syntax

array array_flip ( array $array )

Parameters

$array

: The array whose keys and values you want to swap.

Return Value

The function returns the flipped array. Non‑string or non‑integer values in the original array cause a runtime error.

Examples

Example 1

$array = array("a" => 1, "b" => 2, "c" => 3);
$flippedArray = array_flip($array);
print_r($flippedArray);

Output:

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

This demonstrates swapping a simple associative array where numeric values become keys.

Example 2

$array = array("apple" => "red", "banana" => "yellow", "orange" => "orange", "grape" => "purple");
$flippedArray = array_flip($array);
print_r($flippedArray);

Output:

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

Here the fruit names are keys and their colors become values; after flipping, colors become keys.

Example 3

$array = array(1 => "a", 2 => "b", 3 => "c", 4 => "a");
$flippedArray = array_flip($array);
print_r($flippedArray);

Output:

Array
(
    [a] => 4
    [b] => 2
    [c] => 3
)

When duplicate values exist, the resulting array keeps the last key encountered for each value.

Conclusion

The array_flip() function is a practical tool for quickly swapping keys and values in PHP arrays, but it requires that original values be strings or integers to avoid errors.