Duplicate rows of a 2d array to represent each date within the start and end date values of the row

I have the following array called $exhibitions:

Array
(
    [0] => Array
        (
            [exhibition_title] => Picasso
            [venue_name] => Gallery 1
            [room_name] => Room 4
            [start_date] => 2023-11-15
            [end_date] => 2023-12-10
            [room_id] => 261
            [exhibition_id] => 3540
            [venue_order] => 2
        )

    [1] => Array
        (
            [exhibition_title] => Monet
            [venue_name] => Gallery 4
            [room_name] => Room 2
            [start_date] => 2023-10-01
            [end_date] => 2023-11-13
            [room_id] => 274
            [exhibition_id] => 8417
            [venue_order] => 1
        )
)

What I need to do is use the start_date and end_date to create a range of dates each exhibition is open, and then for each of those dates essentially duplicate the rest of the information in the existing sub-array with the individual date appended to the end of the sub-array. My desired output would be:

I saw this similar post and modified it so that instead of echoing the $given_date, it added it to the array in a new column called "date".

foreach ($exhibitions as $key => $value) {

    $startDate = strtotime($value['start_date']);
    $endDate = strtotime($value['end_date']);

    // Loop between timestamps, 24 hours at a time
    for ($i = $startDate; $i <= $endDate; $i = $i + 86400 ) {
            $given_date = date('Y-m-d', $i );     
            $exhibitions[$key]['date'] = $given_date;
    }    

};

The problem was that instead of adding one date per date in the date range, it added the last date in the range only. When I echoed the $given_date just to make sure it was iterating each date, it lists every date in the range, so I'm assuming there's something wrong with how I added the new column but I can't figure out what.

Solution

Iterate your input array's rows and access the start and end dates.
Create an iterable payload of dates using PHP's native DateTime methods.
Loop over those dates, append the individual date to the row data, then pass the extended row into the result array.

To have an "inclusive" range of dates, add 1 day to the end date (otherwise every range will be one day short).

By appending the generated date to the row data with the union operator (+), you avoid needing to write out every element in the row while pushing.

Code: (Demo)

$result = [];
foreach ($exhibitions as $row) {
    $dateRange = new DatePeriod(
        new DateTime($row['start_date']),
        new DateInterval('P1D'),  // 1 day per step
        new DateTime("{$row['end_date']} +1 day")  // +1 day to include end date
    );
    foreach ($dateRange as $d) {
        $result[] = $row + ['date' => $d->format("Y-m-d")];
    }
}
var_export($result);

...from PHP8.2, you can use a special flag instead of +1 day. (Demo)

$dateRange = new DatePeriod(
    new DateTime($row['start_date']),
    new DateInterval('P1D'),
    new DateTime($row['end_date']),
    DatePeriod::INCLUDE_END_DATE
);