VB Subset Example

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Imports System
Imports System.Collections

Imports CenterSpace.NMath.Core
Imports System.IO

Namespace CenterSpace.NMath.Core.Examples.VisualBasic

  ' A .NET example in Visual Basic showing how to access arbitrary subsets of a data frame.

  ' In addition to accessors for individual elements, columns, or rows in
  ' a data frame, class DataFrame provides a large number of indexers and
  ' member functions for accessing sub-frames containing any arbitrary subset
  ' of rows, columns, or both. Such indexers and methods accept the NMath Core
  ' types Slice and Range to indicate sets of row or column indices with constant
  ' spacing. In addition, NMath Stats introduces a new class called Subset.
  ' Like a Slice or Range, a Subset represents a collection of indices that can be
  ' used to view a subset of data from another data structure. Unlike a Slice or
  ' Range, however, a Subset need not be continuous, or even ordered. It is
  ' simply an arbitrary collection of indices.

  Module SubsetExample

    Sub Main()

      ' Read in data from the file. The data comes from The Data and Story 
      ' Library (http:'lib.stat.cmu.edu/DASL) and is described below:
      ' These data measure protein consumption in twenty-five European
      ' countries for nine food groups. 
      Dim DF As DataFrame = DataFrame.Load("SubsetExample.dat")

      Console.WriteLine("COMPLETE DATA SET")

      ' Subset instances can be constructed in a variety of ways. One constructor
      ' simply accepts an array of integers. The integers do not need to be ordered.
      Dim Subset1 As Subset = New Subset(New Integer() {5, 4, 0, 3})

      ' Let's use this subset to get a sub-frame of the data. This code gets rows
      ' 5, 4, 0, and 3 from the original data frame, in that order, and all columns.
      Console.WriteLine("ARBITRARY SUBSET OF ROWS")

      ' This code gets uses the same subset to get columns 5, 4, 0, and 3 from the
      ' original data frame, in that order, and all rows.
      Console.WriteLine("ARBITRARY SUBSET OF COLUMNS")

      ' Indexers enable you to subset both rows and columns simultaneously.
      Console.WriteLine(DF(Subset1, Subset1))

      ' A very useful constructor takes an array of boolean values and constructs a
      ' Subset containing the indices of all true elements in the array. Let's create
      ' a subset of row indices containing those rows where protein from Milk exceeds
      ' protein from Fish.
      Dim BArray(DF.Rows) As Boolean

      Dim I As Integer

      For I = 0 To DF.Rows - 1
        BArray(I) = CType(DF("Milk")(I), Double) > CType(DF("Fish")(I), Double)
      Dim MilkGTFish As Subset = New Subset(BArray)
      Console.WriteLine("ROWS WHERE MILK > FISH")

      ' The StatsFunctions.If() method applies a given logical function delegate to 
      ' a data set and returns an array of boolean values. Let's create a subset for
      ' countries where protein consumption from Nuts exceeds 3.0. See below for
      ' the definition of logical function GT3().
      BArray = StatsFunctions.If(DF("Nuts"), New Func(Of Double, Boolean)(AddressOf GT3))
      Dim NutsGT3 As Subset = New Subset(BArray)
      Console.WriteLine("ROWS WHERE NUTS > 3.0")

      ' The Subset class provides a variety of operators for combining subsets, including
      ' operator& for intersections and operator| for unions. 
      Console.WriteLine("ROWS WHERE (MILK > FISH) AND (NUTS > 3.0)")
      Console.WriteLine(DF.GetRows(Subset.Intersection(MilkGTFish, NutsGT3)))

      Console.WriteLine("ROWS WHERE (MILK > FISH) OR (NUTS > 3.0)")
      Console.WriteLine(DF.GetRows(Subset.Union(MilkGTFish, NutsGT3)))

      Console.WriteLine("Press Enter Key")

    End Sub

    Function GT3(ByVal X As Double) As Boolean
      Return (X > 3.0)
    End Function

  End Module

End Namespace
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