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Imports System
Imports System.Text
Imports System.Collections
Imports Microsoft.VisualBasic
Imports CenterSpace.NMath.Core
Imports System.IO
Namespace CenterSpace.NMath.Examples.VisualBasic
A .NET example in Visual Basic showing how to use the cross-tabulation functionality of DataFrame.
As illustrated in the FactorExample, the DataFrame.GetFactor() method can be used
in conjunction with Subset.GetGroupings() to access "cells" of data based on one
or two grouping factors. This is such a common operation that class DataFrame also
provides the Tabulate() methods as a convenience. This method accepts one or two
grouping columns, a data column, and a delegate to apply to each data column subset.
The results are returned in a new data frame.
Module CrossTabulationExample
Sub Main()
Read in data from the file. The data show test scores for 18 children on a
simple reading test. The childs gender ("male" or "female") and grade
(4, 5, or 6) is also recorded.
Dim DF As DataFrame = DataFrame.Load("CrossTabulationExample.dat", True, False, ControlChars.Tab, True)
Console.WriteLine()
Console.Write(DF)
Console.WriteLine()
Console.WriteLine()
This code encapsulates the static StatsFunctions.Mean() function in a
Func(Of IDFColumn, Double) delegate, then displays the average
test score for each grade:
Dim Mean As New Func(Of IDFColumn, Double)(AddressOf StatsFunctions.Mean)
Console.WriteLine(DF.Tabulate("Grade", "Score", Mean))
Console.WriteLine()
The code shows the average test score for every combination of gender and grade:
Dim Means As DataFrame = DF.Tabulate("Grade", "Gender", "Score", Mean)
Console.WriteLine(Means)
Console.WriteLine()
The returned data frame can be easily accessed for individual results:
Console.WriteLine("Average score for boys in grade 5 = " & Means(5, "male"))
Console.WriteLine("Average score for grade 5 = " & Means(5, "Overall"))
Console.WriteLine("Average score for boys = " & Means("Overall", "male"))
Console.WriteLine("Grand average = " & Means("Overall", "Overall"))
Console.WriteLine()
Most of the static descriptive statistics functions on class StatsFunctions
accept an IDFColumn and return a double. A few return integers. For example,
this code encapsulates StatsFunctions.Count(), which returns the number of items
in a column, in a Func(Of IDFColumn, Int), then displays the number
of subjects in each cell:
Dim Count As New Func(Of IDFColumn, Integer)(AddressOf StatsFunctions.Count)
Console.WriteLine(DF.Tabulate("Grade", "Gender", "Score", Count))
Console.WriteLine()
The delegate the returns a generic object can be especially useful if you want to
tabulate a variety of summary statistics all at once:
Dim GetSummaryDelegate As New Func(Of IDFColumn, Object)(AddressOf CrossTabulationExample.GetSummary)
Dim SummaryStats As DataFrame = DF.Tabulate("Grade", "Gender", "Score", GetSummaryDelegate)
Console.WriteLine("Summary Statistics for Boys in Grade 6")
Console.WriteLine(SummaryStats(6, "male"))
Console.WriteLine()
Console.WriteLine("Press Enter Key")
Console.Read()
End Sub
Function GetSummary(ByVal Data As IDFColumn) As Object
Dim MySummary As Summary = New Summary
MySummary.N = StatsFunctions.Count(Data)
MySummary.Mean = StatsFunctions.Mean(Data)
MySummary.StDev = StatsFunctions.StandardDeviation(Data)
MySummary.Min = StatsFunctions.MinValue(Data)
MySummary.Max = StatsFunctions.MaxValue(Data)
Return MySummary
End Function
End Module
Public Class Summary
Public N As Integer
Public Mean As Double
Public StDev As Double
Public Min As Double
Public Max As Double
Overrides Function ToString() As String
Dim NL As String = System.Environment.NewLine
Dim Buff As StringBuilder = New StringBuilder()
Buff.Append("Size = " & N & NL)
Buff.Append("Mean = " & Mean & NL)
Buff.Append("Standard Deviation = " & StDev & NL)
Buff.Append("Minimum = " & Min & NL)
Buff.Append("Maximum = " & Max & NL)
Return Buff.ToString()
End Function
End Class
End Namespace
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