VB Missing Values Example

Imports System


Imports System.IO

Namespace CenterSpace.NMath.Examples.VisualBasic

  A .NET example in Visual Basic showing how to manipulate data that has missing values.
  Module MissingValuesExample

    Sub Main()

      In the data, missing values are denoted by -1. Set the defaults
      accordingly.
      StatsSettings.IntegerMissingValue = -1

      Read in data from a tab-delimited file. Data has fields for name, manufacturer,
      type, calories, protein, fat, sodium, fiber, carbohydrates, sugars, potassium,
      vitamins, shelf weight, cups, rating, age, gender and grade.
      Dim Data As DataFrame = DataFrame.Load("MissingValuesExample.dat")

      Print out initial data. 
      Console.WriteLine()
      Console.WriteLine(Data)
      Console.WriteLine()

      Check how many missing values are in each numeric column
      Dim Total As Integer = Data.Rows
      Dim Valid As Integer
      Dim C As Integer
      For C = 0 To Data.Cols - 1
        If Data(C).IsNumeric Then
          Console.Write(Data(C).Label)
          Console.Write(": ")
          Dim NC As Integer = StatsFunctions.NaNCount(Data(C))
          Valid = Total - NC
          Console.WriteLine(Valid)
        End If
      Next
      Console.WriteLine()

      The columns "carbo", "sugars" and "potass" contain missing values.
      We can still perform descriptive statistics on them.
      Console.WriteLine("Average sugar content: " + StatsFunctions.NaNMean(Data("sugars")).ToString("G5"))

      Sorting routines give ambiguous results when columns contain NaN values.
      We can strip the missing values first.
      Dim Stripped As DFIntColumn = CType(StatsFunctions.NaNRemove(Data("sugars")), DFIntColumn)
      Console.WriteLine("Median sugar content: " + StatsFunctions.Median(Stripped).ToString("G5"))
      Console.WriteLine("90th percentile sugar content: " + StatsFunctions.Percentile(Stripped, 0.9).ToString("G5"))
      Console.WriteLine()

      Create a sub-frame that contains only rows without missing values.
      Dim CleanData As DataFrame = Data.CleanRows()

      Console.WriteLine("Stripped " & (Data.Rows - CleanData.Rows) & " rows containing missing values.")

      Console.WriteLine()
      Console.WriteLine("Press Enter Key")
      Console.Read()

    End Sub
  End Module
End Namespace