Solve PHP reindex array: single and multi-dimensional arrays

Sometimes, your PHP code will create an array that has gaps in its keys as shown below:

Array
(
    [1] => Nathan
    [6] => Jack
    [10] => Jessie
)

In the above example, the array keys are unordered as it goes from 1 to 6 to 10.

To reindex the array keys of the array, you need to call the arra_values() function on your array.

See the code example below:

<?php
$arr = [
    1 => "Nathan",
    6 => "Jack",
    10 => "Jessie",
];

$arr = array_values($arr);

print_r ($arr);

The print_r output will be:

Array
(
    [0] => Nathan
    [1] => Jack
    [2] => Jessie
)

Reindex a multi-dimensional array

The array_values() only works for a single-dimension array.

When you need to reindex a multi-dimensional array, you need to call the array_map() function and pass array_values as its first parameter:

<?php
$arr = [
    1 => [
        4 => "Nathan",
        5 => "PHP developer"
    ],
    6 => [
        4 => "Jack",
        5 => "JavaScript developer"
    ]
];

// 👇 reindex the child arrays
$arr = array_map("array_values", $arr);

print_r ($arr);

The output will be:

Array
(
    [1] => Array
    (
        [0] => Nathan
        [1] => PHP developer
    )

    [6] => Array
    (
        [0] => Jack
        [1] => JavaScript developer
    )
)

Note that only the child arrays are being reindexed with the array_map().

This is because the array_map() function runs the array_values() function for each child element of the array.

To reindex both parent and child arrays, you need to call array_values() again:

$arr = array_map("array_values", $arr);
$arr = array_values($arr);

Now both parent and child array keys will be reset:

(
    [0] => Array
    (
        [0] => Nathan
        [1] => PHP developer
    )

    [1] => Array
    (
        [0] => Jack
        [1] => JavaScript developer
    )

)

But keep in mind that this trick won’t work when you have an unstructured array.

Suppose you have an array with the following structure:

$arr = [
    1 => [
        4 => "Nathan",
        5 => "PHP developer"
    ],
    6 => [
        4 => "Jack",
        5 => "JavaScript developer"
    ],
    10 => "Jessie",
];

Calling the array_map() function will result in a fatal error:

PHP Fatal error:  Uncaught TypeError: array_values(): 
Argument #1 ($array) must be of type array, string given in ...
Stack trace:
#0 [internal function]: array_values('Jessie')

To reindex an unstructured multi-dimensional array, you need to create a custom function.

This function needs to loop over the array and call array_values() on all values that are an array type.

The function below should be good:

function array_reset(array $arr)
{
    $arr = array_values($arr);
    foreach ($arr as $k => $v) {
        if (is_array($v)){
            $v = array_reset($v);
            $arr[$k] = $v;
        }
    }
    return $arr;
}

Let’s test running the arra_reset() function:

<?php
$arr = [
    1 => [
        4 => "Nathan",
        5 => "PHP developer"
    ],
    6 => [
        4 => "Jack",
        5 => "JavaScript developer"
    ],
    10 => "Jessie",
];

// 👇 reindex the array
$arr = array_reset($arr);

print_r ($arr);

The code above produces the following output:

Array
(
    [0] => Array
    (
        [0] => Nathan
        [1] => PHP developer
    )

    [1] => Array
    (
        [0] => Jack
        [1] => JavaScript developer
    )

    [2] => Jessie
)

As you can see, both parent and child arrays are reindexed using the array_reset() function.

This function is also able to reset the index of unstructured arrays, where the array value can be a non-array.

Feel free to use the array_reset() function in your code.

Now you’ve learned how to reindex a PHP array and reset its keys. Great job! 👍

Reindex a multi-dimensional array

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