PHP empty key in array

Question

In PHP, is there a function for finding the lowest numerical key without a value in an array? I have an array like this:

array (
    0 => 'nested array',
    1 => 'nested array',
    2 => 'nested array',
    3 => 'nested array',
    6 => 'nested array',
    7 => 'nested array',
)

and I would like to add a value to this array (at 4), not necessarily unique, and get its position back without altering the rest of the keys. Is the easiest way to loop through the array and test isset(), or is there an easier way?

Generate the keys you expect with range, then find the lowest missing one. $expected_keys = range(0, count($your_array) - 1); $missing_keys = array_diff($expected_keys, array_keys($your_array)); return min($missing_keys); — user1233508
– user1233508, Commented Feb 23, 2014 at 11:26

Darragh Enright · Accepted Answer · 2014-02-23 11:43:21Z

4

You could try the following to search for the lowest key:

$arr = array (
    0 => 'nested array',
    1 => 'nested array',
    2 => 'nested array',
    3 => 'nested array',
    6 => 'nested array',
    7 => 'nested array',
);

// get a list of existing keys
$keys = array_keys($arr);

// get the min and max keys
$min = min($keys);
$max = max($keys);

// get the missing keys by:
// * creating a range from the existing min/max
// *diff it from the list of actual keys
$missing = array_diff(range($min, $max), $keys);

// get the min missing key from the diff
echo min($missing);

Hope this helps :)

edited Feb 23, 2014 at 11:43

answered Feb 23, 2014 at 11:28

Darragh Enright

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5 Comments

Shankar Narayana Damodaran Over a year ago

+1 for the easy way.

Amal Over a year ago

+1 for the comments. Not to be pedantic, but I think you should rename $key to $keys ;)

salathe Over a year ago

How is this any easier than looping to find an available key?

Darragh Enright Over a year ago

hi @salathe - I assume you're addressing Shankar with that question. I don't think it is necessarily, there's more than one way to skin a cat I suppose :) I personally have nothing against a loop, this is just my approach.

salathe Over a year ago

@Darragh I was addressing you, since the question is asking for the "easiest" way.

salathe · Accepted Answer · 2014-02-23 12:10:06Z

3

In PHP, is there a function for finding the lowest numerical key without a value in an array?

No.

Is the easiest way to loop through the array and test isset()

Looping is okay, but isset() isn't going to be the best choice. It could raise a false-positive where an array key exists but contains a NULL value. A better choice would be array_key_exists().

In your case, a loop can be as simple as:

for ($key = 0; array_key_exists($key, $arr); $key++);
var_dump($key);

or is there an easier way?

See the other answers suggesting alternatives, which may or may not be easier.

edited Feb 23, 2014 at 12:10

answered Feb 23, 2014 at 12:02

salathe

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Comments

Kamehameha · Accepted Answer · 2014-02-23 11:26:56Z

0

This works -

function find_empty($arr){
    foreach(range(0,max(array_keys($arr))) as $i){
        if(!array_key_exists($i, $arr)){
            return $i;
        }
    }
    return -1;
}

Testing it -

$arr = array (
    0 => 'nested array',
    1 => 'nested array',
    2 => 'nested array',
    3 => 'nested array',
    6 => 'nested array',
    7 => 'nested array',
);
var_dump(find_empty($arr));
/**
OUTPUT
int 4
**/

answered Feb 23, 2014 at 11:26

Kamehameha

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Comments

Rudie · Accepted Answer · 2014-02-23 11:28:44Z

0

You could do something like this. I think it looks cool, but I wouldn't do it, because it's not very efficient:

$array = array(0 => 'x', 1 => 'x', 2 => 'x', 4 => 'x', 7 => 'x');

$indexes = array_keys($array); // 0, 1, 2, 4, 7
// sort($array, SORT_NUMERIC);
$all_indexes = range($indexes[0], $indexes[count($indexes)-1]); // 0, 1, 2, 3, 4, 5, 6, 7
$missing_indexes = array_diff($all_indexes, $indexes); // 3, 5, 6
print_r($missing_indexes);

$lowest = reset($missing_indexes);
$highest = end($missing_indexes);
var_dump($lowest, $highest);

You can compact it in many less lines if that's your thing.

You now have all the missing index information: how many, which, lowest, highest, average etc

answered Feb 23, 2014 at 11:28

Rudie

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1 Comment

Amal Over a year ago

I'd rather use min() and max() to get the minimum and maximum values (you don't need the sort() that way).

Anthony · Accepted Answer · 2014-02-23 11:31:26Z

0

You can get an array of all open keys by using range() and array_diff along with array_keys:

$array = array (
    0 => 'nested array',
    1 => 'nested array',
    2 => 'nested array',
    3 => 'nested array',
    6 => 'nested array',
    7 => 'nested array',
);

$array_keys = array_keys($array);
sort($array_keys);

$min_key = 0;
$max_key = end($array_keys);

$array_key_range = range($min_key, $max_key);

$open_keys = array_diff($array_key_range , $array_keys);

You can then use the first value in that array as the lowest, or any, if you just want to find an open slot.

answered Feb 23, 2014 at 11:31

Anthony

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