VB Subset Example

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Imports System
Imports System.Collections

Imports CenterSpace.NMath.Core

Imports System.IO

Namespace CenterSpace.NMath.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})

      Lets 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. Lets 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. Lets 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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