anchor.diff:      RowSeries<_, _>.FromSeries(Series.dropMissing res) 
   
     /// [category:Accessors and slicing]
  -  member frame.Rows =    
  +  member frame.Rows : RowSeries<'TRowKey, 'TColumnKey> =    
       // This operation needs to work on virtualized frames (by returning a
       // virtualized series) and it also needs to be efficient for in-memory frames.
       // We do this by creating `Combine([...], NaryTransform.RowReader)` command - 
  
positive.code:     ColumnSeries(Series(columnIndex, newData, vectorBuilder, indexBuilder))
  
    /// [category:Accessors and slicing]
    member frame.RowsDense = 
      // Create an in-memory series that contains `ObjectSeries` for each
      // row that has a value for each column. This returns an in-memory
      // series because we do not know how many rows we'll need to return.
  
negative.code:   member x.Item with get(items) = x.GetItems(items) |> FrameUtils.fromRows indexBuilder vectorBuilder 
    member x.Item with get(level) = x.GetByLevel(level)
  
    /// Creates a `RowSeries` from a filtered series
    /// (and implements slicing in terms of the specified series)  
    static member FromSeries(series:Series<'TRowKey, ObjectSeries<'TColumnKey>>) =
      { new RowSeries<'TRowKey, 'TColumnKey>(series.Index, series.Vector, series.VectorBuilder, series.IndexBuilder) with
          override x.GetSlice(lo, hi) = 
            x.BaseGetSlice(lo, hi) 
  