Why is Frame.tryValues ​​failing with this simple example?

Help for Frame.tryValues

has the following:

"Given a data frame containing columns of the type tryval<'T>

, returns a new data frame that contains the underlying values ​​of the type 'T

."

I interpreted this to mean that the function will split the type tryval

into values ​​and return those separated values. Perhaps I did not understand the text, because the function does not work in the following case:

let dates  = 
  [ DateTime(2013,1,1); 
    DateTime(2013,1,2); 
    DateTime(2013,1,3) ]

let values = [ 10.0; 20.0; 30.0 ]

let first = Series(dates, values)

let frame = Frame(["first"], [first])

let f (dt: DateTime) (row: ObjectSeries<string>) = row.Get("first") :?> double

let s =
    frame
    |> Frame.tryMapRows f

// frame1 second column has tryvalues
let frame1 = Frame(["first"; "second"], [first; s])
// frame2 has no tryvalues
let frame2 = Frame(["first"; "second"], [first; first])

let frame3 =
    frame1
    |> Frame.tryValues
// fails

let frame3 =
    frame2
    |> Frame.tryValues
// Ok, works fine

      

        
        
        
      

    

Why Frame.tryValues

does the first call above fail and the second not?