code: def _stack_positions(positions, pos_in_dollars=True):
      
      if pos_in_dollars:
          # convert holdings to percentages
          positions = get_percent_alloc(positions)
  
      # remove cash after normalizing positions
      positions = positions.drop('cash', axis='columns')
  
      # convert positions to long format
      positions = positions.stack()
      positions.index = positions.index.set_names(['dt', 'ticker'])
  
      return positions
docs: Convert positions to percentages if necessary, and change them
      to long format.
  
      Parameters
      ----------
      positions: pd.DataFrame
          Daily holdings (in dollars or percentages), indexed by date.
          Will be converted to percentages if positions are in dollars.
          Short positions show up as cash in the 'cash' column.
  
      pos_in_dollars : bool
          Flag indicating whether `positions` are in dollars or percentages
          If True, positions are in dollars.