Replace recurring values of a flat array with an empty string

I am populating an array of dates from two sources: an array of dates and a range of dates between two dates.

$dateann = ['2024-08-16', '2024-08-11', '2024-08-16', '2024-09-16'];
$period = CarbonPeriod::between('2024-08-01', '2024-08-31');
foreach ($period as $date) {
    $days[] = $date->format('Y-m-d');
}
$array_dates = array_merge($dateann, $days);

This can result in duplicate dates in the merged array. I would like to replace any recurring dates with an empty string.

Current output:

array: [
  0 => "2024-08-16"
  1 => "2024-08-11"
  2 => "2024-08-16"
  3 => "2024-09-05"
  4 => "2024-08-01"
  5 => "2024-08-02"
  6 => "2024-08-03"
  7 => "2024-08-04"
  8 => "2024-08-05"
  9 => "2024-08-06"
  10 => "2024-08-07"
  11 => "2024-08-08"
  12 => "2024-08-09"
  13 => "2024-08-10"
  14 => "2024-08-11"
  15 => "2024-08-12"
  16 => "2024-08-13"
  17 => "2024-08-14"
  18 => "2024-08-15"
  19 => "2024-08-16"
  20 => "2024-08-17"
  21 => "2024-08-18"
  22 => "2024-08-19"
  23 => "2024-08-20"
  24 => "2024-08-21"
]

Desired output:

array: [
    0 => "2024-08-16"
    1 => "2024-08-11"
    2 => ""
    3 => "2024-09-05"
    4 => "2024-08-01"
    5 => "2024-08-02"
    6 => "2024-08-03"
    7 => "2024-08-04"
    8 => "2024-08-05"
    9 => "2024-08-06"
    10 => "2024-08-07"
    11 => "2024-08-08"
    12 => "2024-08-09"
    13 => "2024-08-10"
    14 => ""
    15 => "2024-08-12"
    16 => "2024-08-13"
    17 => "2024-08-14"
    18 => "2024-08-15"
    19 => ""
    20 => "2024-08-17"
    21 => "2024-08-18"
    22 => "2024-08-19"
    23 => "2024-08-20"
    24 => "2024-08-21"
]

Check if the current index is the same as the first index of the value. If not, replace the value with an empty string.

foreach ($array_dates as $index => $value) {
    if (array_search($value, $array_dates) != $index) {
        $array_dates[$index] = '';
    }
}