Map two associative arrays which have different sizes/keys

I want to merge 2 arrays together but I want it in a specific way.
The first array are the dates I want to filter with the second array dates.

$first = [
    '2022-10-23' => '2022-10-23',
    '2022-10-24' => '2022-10-24',
    '2022-10-25' => '2022-10-25',
    '2022-10-26' => '2022-10-26',
    '2022-10-27' => '2022-10-27',
    '2022-10-28' => '2022-10-28',
    '2022-10-29' => '2022-10-29'
];

$second = [
    '2022-10-24' => [
        'id' => 11,
        'user_id' => 1,
        'notitie' => 'Mag al helemaal niet',
        'datum' => '2022-10-24',
        'user_role' => 'client'
    ],
    '2022-10-26' => [
        'id' => 15,
        'user_id' => 1,
        'notitie' => 26,
        'datum' => '2022-10-26',
        'user_role' => 'client'
    ],
];

This is the result I want:

Array
(
    [2022-10-23] => Array
        (
            [1] => 
        )

[2022-10-24] => Array
    (
        [id] => 11
        [user_id] => 1
        [notitie] => Mag al helemaal niet 
        [datum] => 2022-10-24
        [user_role] => client
    )
    
[2022-10-25] => Array
    (
        [1] => 
    )

[2022-10-26] => Array
    (
        [id] => 15
        [user_id] => 1
        [notitie] => 26
        [datum] => 2022-10-26
        [user_role] => client
    )

[2022-10-27] => Array
    (
        [1] => 
    )

[2022-10-28] => Array
    (
        [1] => 
    )

[2022-10-29] => Array
    (
        [1] => 
    )

)

 // My coding attempt

if ($agendaButtonInfo == "timeGridWeek"){


  $userNotities = array();
  $dagenTussen = array();

  $period = new DatePeriod(
    new DateTime($agendaDatumBegin),
    new DateInterval('P1D'),
    new DateTime($agendaDatumEinde)
);

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

  
  $dagenTussen[$value->format('Y-m-d')] =  $value->format('Y-m-d');

  
}


  $stmt = $pdo->query("SELECT notitie_client.id, notitie_client.user_id, notitie_client.notitie, notitie_client.datum, user.user_role
  FROM (notitie_client 
  INNER JOIN user ON notitie_client.user_id = user.id) 
  WHERE notitie_client.user_id='$userId' AND notitie_client.datum BETWEEN '$agendaDatumBegin' AND '$agendaDatumEinde' ORDER BY notitie_client.datum ASC;");
  
  if ($stmt->rowCount() > 0) {
    while ($row = $stmt->fetch()) {
 
      /*
      
      echo "<pre>";
        print_r ($row);
        echo "</pre>";
      */ //$userNotitiess[] = array("datumm" => $row["datum"]);
      $userNotities[$row["datum"]] = array( "id" => $row["id"], "user_id" => $row["user_id"], "notitie" => $row["notitie"], "datum" => $row["datum"], "user_role" => $row["user_role"]);

    }
  }


 
  



echo "<pre>";

print_r($dagenTussen);
echo "<pre>";
print_r($userNotities);

/*
print_r  ($dagenTussen);

  
  function myfunction($v1,$v2)
  {
    //print_r ($v2);
   
  
  if ($v1===$v2["datum"])
    {
    return "same";
    }else{
  return "different";
  }
  }

  echo "<pre>";
  print_r(array_map("myfunction",$dagenTussen, $userNotities));
  //print_r(array_merge($dagenTussen,$userNotities));

  /*
  foreach($userNotities as $userNotitie ){
    echo "<pre>";
    print_r ($userNotitie);
    echo "</pre>";
  }
*/
$testt = array("wesley", "darlon");
$people = array("Peter", "Joe", "wesley", "darlon");

//print_r ($userNotities);


foreach ($userNotities as $notatie){
  echo "<pre>";
  

  $notatieDatum[] = $notatie["datum"];

}

print_r ($notatieDatum);



$eindArray = array();



foreach ($dagenTussen as $dag){

  echo "<br>";

  if (in_array($dag, $notatieDatum))
  {
  echo "Match found";
  print_r ($userNotities);
  }
else
  {
  echo "Match not found";
  }
}

}

>Solution :

Map the second array values to the first array values.

The null coalescing operator (??) will fallback to a default value when not found in the lookup.

Code: (Demo)

var_export(
    array_map(
        fn($v) => $rows[$v] ?? [],
        $dates
    )
);

Or if for some odd reason you want fallback to those empty 1-keyed elements, use this:

var_export(
    array_map(
        fn($v) => $rows[$v] ?? [1 => ''],
        $dates
    )
);