How to reindex an array?

Question

My array looks like this:

array(
  0 => 'val',
  2 => 'val',
  3 => 'val',
  5 => 'val',
  7 => 'val'
);

How can I reset the keys so it will go like 0, 1, 2, 3, 4?

Answer 1

Use array_values:

$reindexed_array = array_values($old_array);

Answer 2

array_splice($old_array, 0, 0);

It will not sort array and will not create a second array

Answer 3

By using sort($array);

See PHP documentation here.

I'd recommend sort over array_values as it will not create a second array. With the following code you now have two arrays occupying space: $reindexed_array and $old_array. Unnecessary.

$reindexed_array = array_values($old_array);

Answer 4

From PHP7.4, you can reindex without a function call by unpacking the values into an array with the splat operator. Consider this a "repack".

Code: (Demo)

$array = array(
  0 => 'val',
  2 => 'val',
  3 => 'val',
  5 => 'val',
  7 => 'val'
);

$array = [...$array];

var_export($array);

Output:

array (
  0 => 'val',
  1 => 'val',
  2 => 'val',
  3 => 'val',
  4 => 'val',
)

Note: this technique will NOT work on associative keys (the splat operator chokes on these). Non-numeric demo

The breakage is reported as an inability to unpack string keys, but it would be more accurate to say that the keys must all be numeric. Integer as string demo and Float demo

Answer 5

array_splice($jam_array, 0, count($jam_array));

To sort an array with missing intermediate indices, with count the order is more secure. So 0 is the first index and count($jam_array) or sizeof($jam_array) return the decimal position of the array, namely, last index.

Answer 6

It's worth pointing out that the array in the question is a very special case, where all values are the same and keys are already in ascending order. If you have an array with different values and keys in any random order, and you want to sort it by key and reindex the keys, the existing answers will not do what you expect.

For example, if you have something like this:

[
    7 => 'foo',
    0 => 'bar',
    2 => 42
];

and you want to end up with this:

[
    0 => 'bar',
    1 => 42,
    2 => 'foo',
]

you can't just use array_values(), array_splice() or sort(), because you would end up with

[
    0 => 'foo',
    1 => 'bar',
    2 => 42,
]

Instead, you first need to sort the array based on the keys, using ksort(), and then reindex the keys using array_values():

$arr = [
    7 => 'foo',
    0 => 'bar',
    2 => 42
];

ksort($arr, SORT_NUMERIC);
$arr = array_values($arr);

Result:

[
    0 => 'bar',
    1 => 42,
    2 => 'foo',
]

Answer 7

How to remove keys from php array?

was looking for a more elegant solution for this and got redirected here. my not-so-pretty solution might help someone else

you will use a second (temporary/buffer) array that will keep the filtered data

    // main array
    $main_arr = array(
        1      => 'ok',
        2      => 'ok',
        5      => 'discard',
        99     => 'discard',
        'a'    => 'ok',
        'b'    => 'red',
        'text' => 1.22,
        'zzz'  => true
    );

    $temp_arr = array(); // temporary array. will be unset later on
    
    // parse the main array
    foreach( $main_arr as $key => $value ) {
        if( $value != 'discard' ) {
            $temp_arr[$key] = $value; // retain the key=>value pairs
        }
    }
    
    // overwrite $main_arr only if there's a mismatch between the main/temporary arrays' key count
    if( count($main_arr) != count($temp_arr) ) {
        $main_arr = $temp_arr; // replace main array content with data from temporary array
    }
    
    unset($temp_arr); // free (some) memory