Group associative elements by keys with contiguous dates to create an array of associative arrays

For a rent application, I have an array $dates like this:

Array
(
    [2013-07-19] => 1
    [2013-07-21] => 3
    [2013-07-23] => 2
    [2013-07-24] => 4
    [2013-07-25] => 4
    [2013-07-26] => 2
    [2013-07-27] => 2
    [2013-07-30] => 3
    [2013-07-31] => 1
)

The date is the key, and the values are the number of items rent in that day for a specific product

How can I split this array in many sub arrays containing each a list of consecutive days? Like this:

Array
(

    [0] => Array
        (
            [2013-07-19] => 1
        )

    [1] => Array
        (
            [2013-07-21] => 3
        )

    [2] => Array
        (
            [2013-07-23] => 2
            [2013-07-24] => 4
            [2013-07-25] => 4
            [2013-07-26] => 2
            [2013-07-27] => 2
        )

    [3] => Array
        (
            [2013-07-30] => 3
            [2013-07-31] => 1
        )

)

you can do it like this:

$data = array(
  '2013-07-19' => 1,
  '2013-07-21' => 3,
  '2013-07-23' => 2,
  '2013-07-24' => 4,
  '2013-07-25' => 4,
  '2013-07-26' => 2,
  '2013-07-27' => 2,
  '2013-07-30' => 3,
  '2013-07-31' => 1
);

$result = array();
// choose a fake old date or the first date from $data
$ref = new DateTime('1821-11-11');

foreach ($data as $datum => $nb) {
    // compare $ref + 1 day with $datum (the current item date)
    if ($ref->modify('+1 day')->format('Y-m-d') !== $datum) { 
        $result[] = array(); 
        $ref = new DateTime($datum);
    }

    $result[count($result) - 1][$datum] = $nb;
}
print_r($result);

demo

Notices:

• starting with PHP 7.3, you can easily extract the first key of the $data array to create the first reference date using array_key_first (instead of using a fake old date):

  $ref = new DateTime(array_key_first($data));
  
  You can also use the combo reset + key for older versions, it doesn't matter since the foreach loop will reset the array pointer immediately after.

• If you want to avoid the creation of a new DateTime instance each time there is a jump between dates ($ref = new DateTime($datum);), you can choose to only set the already existing instance with:

  $ref->setDate(...explode('-', $datum));
  
  (Not sure it will give you a great advantage in terms of readability or performance, but it's a possibility.)