PHP array_flip Function: How it Works with Examples

PHP array_flip swaps keys with values. It works well when you need values as keys in fast lookups.

What is the array_flip Function in PHP?

The array_flip function swaps all keys with values in an array. The result holds values as keys and keys as values.

The syntax looks like this:

array_flip(array $array)

• It takes one parameter: an array with key and value pairs.
• It returns a new array with swapped keys and values.

You can use array_flip to switch keys and values. It works best when you need values as keys for fast checks or mappings.

Here is a quick example:

$data = ["a" => 1, "b" => 2];
$result = array_flip($data);
print_r($result);

Here is the output:

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

It swaps the values with keys and returns the new array.

The function loops through each element. It sets the value as the new key. It then sets the key as the new value.

If two or more values match, the last one replaces the others. The function cannot hold duplicate keys. Only the last pair stays in the final array.

Examples of array_flip in PHP

Here is an example:

$colors = ["red" => 1, "blue" => 2, "green" => 3];
$result = array_flip($colors);
print_r($result);

This shows the swap of color names with numbers. Each value turns into the new key and each key turns into the new value. Here is the output:

Array
(
    [1] => red
    [2] => blue
    [3] => green
)

Here is another example:

$letters = ["x" => 10, "y" => 20, "z" => 20];
$result = array_flip($letters);
print_r($result);

This shows the effect of duplicate values. The key for “y” is lost because “z” also holds 20. The last one replaces the earlier one.

The output:

Array
(
    [10] => x
    [20] => z
)

You can also flip an array with mixed keys. Here is an example:

$data = [100 => "cat", 200 => "dog", 300 => "bird"];
$result = array_flip($data);
print_r($result);

This swaps numbers with animal names. Each number becomes a new value and each name becomes a new key.

The output:

Array
(
    [cat] => 100
    [dog] => 200
    [bird] => 300
)

Wrapping Up

In this article you learned what array_flip does and how it swaps keys with values. You also saw what happens with duplicates and how mixed keys behave.

Here is a quick recap:

• array_flip swaps all keys and values.
• It returns a new array after the swap.
• Duplicate values overwrite earlier keys.
• You can flip arrays with numbers, text, or boolean values.

FAQs

$data = ["a" => 1, "b" => 2, "c" => 3];
$result = array_flip($data);
print_r($result);

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

$data = ["x" => 1, "y" => 1, "z" => 2];
$result = array_flip($data);
print_r($result);

Array
(
    [1] => y
    [2] => z
)

$data = ["x" => [1,2], "y" => 3];
$result = array_flip($data);

$items = ["apple", "banana", "apple", "orange"];
$result = array_keys(array_flip($items));
print_r($result);

Array
(
    [0] => apple
    [1] => banana
    [2] => orange
)

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