DataFrame with fixed columns

open System
open System.IO
open Microsoft.Data.Analysis

let columns : DataFrameColumn array =
    [|
        UInt16DataFrameColumn("VNR", 6L)
        ByteDataFrameColumn("Volume", 10L)
        SingleDataFrameColumn("Value", 12L)
        ByteDataFrameColumn("Farmacy number", 4L)
        PrimitiveDataFrameColumn<DateTime>("Date of sale", 8L)
        CharDataFrameColumn("Sale period", 1L)
        ByteDataFrameColumn("Hospital number", 7L)
        StringDataFrameColumn("Delivery address", 4L)
        StringDataFrameColumn("Wholesaler", 9L)
    |]

use stream =
    new FileStream(
        @"file.txt",
        FileMode.Open, FileAccess.Read, FileShare.Read)

let reader = new TextFieldParser (stream)
reader.TextFieldType <- FieldType.FixedWidth
let widths = columns |> Array.map (fun c -> c.Length |> int)
reader.SetFieldWidths widths

let df = DataFrame columns

while not <| reader.EndOfData do
    try
        let currentRow = reader.ReadFields ()
        df.Append(currentRow |> Seq.map box, true) |> ignore
        //printfn "%A" currentRow
    with ex -> printfn "%s" ex.Message

Console.WriteLine df

(*
Line let df = DataFrame columns
System.ArgumentException: Column lengths are mismatched (Parameter 'column')
   at Microsoft.Data.Analysis.DataFrameColumnCollection.InsertItem(Int32 columnIndex, DataFrameColumn column)
   at Microsoft.Data.Analysis.DataFrameColumnCollection..ctor(IEnumerable`1 columns, Action columnsChanged)
   at Microsoft.Data.Analysis.DataFrame..ctor(DataFrameColumn[] columns)
*)