How to clean a specific index array?

I want to clean a specific index of array, in particular I've 3 index:

0: 
   Appointments
   Unavailables
1:
   Appointments
   Unavailables
2:
   Appointments
   Unavailables

Now I want maintain the first appointments as 0 index. So this is my code:

foreach($appointments as $key => value)
{ 
   if($key != 0)
   {
      unset($appointments[$key]['appointments']);    
   }
}

but unset delete also the key so the final result that I get is:

0: 
   Appointments
   Unavailables
1:
   Unavailables
2:
   Unavailables

I want maintain the appointments object, just I need to empty it's content.
How I can achieve this result?