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Imports System
Imports System.Collections
Imports CenterSpace.NMath.Core
Namespace CenterSpace.NMath.Examples.VisualBasic
A .NET example in Visual Basic showing how to manipulate data using the DataFrame class.
The statistical functions in NMath Stats support the NMath Core types
DoubleVector and DoubleMatrix, as well as simple arrays of doubles. In many
cases, these types are sufficient for storing and manipulating your
statistical data. However, they suffer from two limitations: they can only
store numeric data, and they have limited support for adding, inserting, removing,
and reordering data. Therefore, NMath Stats provides the DataFrame class which
represents a two-dimensional data object consisting of a list of columns of the
same length. Columns are themselves lists of different types of data: numeric,
string, boolean, generic, and so on.
Module DataFrameExample
Sub Main()
Create an empty data frame.
Dim Data As New DataFrame()
Add some columns. These data describe the relationship between
the size of acorns and various oak tree species. Columns in a data frame
can be accessed by numeric index (0...n-1) or by a name supplied at
construction time.
Data.AddColumn(New DFStringColumn("Region"))
Data.AddColumn(New DFNumericColumn("AcornSize"))
Data.AddColumn(New DFNumericColumn("TreeHeight"))
Data.AddColumn(New DFBoolColumn("Threatened"))
Add some rows of data. Rows can be accessed by numeric index (0...n-1)
or by a key object. The first parameter to the AddRow() method, in this
case the name of the oak tree species, is the row key.
Data.AddRow("Quercus alba L.", "Atlantic", 1.4, 27, False)
Data.AddRow("Quercus bicolor Willd.", "Atlantic", 3.4, 21, False)
Data.AddRow("Quercus macrocarpa Michx.", "Atlantic", 9.1, 25, False)
Data.AddRow("Quercus Chapmanii Sarg.", "Atlantic", 0.9, 15, False)
Data.AddRow("Quercus Durandii Buckl.", "Atlantic", 0.8, 23, True)
Data.AddRow("Quercus laurifolia Michx.", "Atlantic", 1.1, 27, False)
Data.AddRow("Quercus marilandica Muenchh.", "Atlantic", 3.7, 9, False)
Data.AddRow("Quercus nigra L.", "Atlantic", 1.1, 24, True)
Data.AddRow("Quercus palustris Muenchh.", "Atlantic", 1.1, 23, False)
Data.AddRow("Quercus texana Buckl.", "Atlantic", 1.1, 9, False)
Data.AddRow("Quercus coccinea Muenchh.", "Atlantic", 1.2, 4, False)
Data.AddRow("Quercus Douglasii Hook. & Arn", "California", 4.1, 18, False)
Data.AddRow("Quercus dumosa Nutt.", "California", 1.6, 6, False)
Data.AddRow("Quercus Engelmannii Greene", "California", 2.0, 17, False)
Data.AddRow("Quercus Garryana Hook.", "California", 5.5, 20, True)
Data.AddRow("Quercus chrysolepis Liebm.", "California", 17.1, 15, False)
Data.AddRow("Quercus vaccinifolia Engelm.", "California", 0.4, 1, False)
Data.AddRow("Quercus tomentella Engelm", "California", 7.1, 18, True)
Display the entire, original data frame.
Console.WriteLine()
Console.WriteLine(Data)
Console.WriteLine()
Reorder some columns. Lets move the AcornSize column to the end.
Data.PermuteColumns(0, 3, 1, 2)
Console.WriteLine(Data)
Console.WriteLine()
If you dont know the index of a column you can query for it by name.
Dim AcornSizeCol As Integer = Data.IndexOfColumn("AcornSize")
Dim treeHeightCol As Integer = Data.IndexOfColumn("TreeHeight")
Sort the rows. Lets sort the rows by AcornSize in ascending order, and secondarily
by TreeHeight in descending order.
Dim ColIndices As Integer() = {AcornSizeCol, treeHeightCol}
Dim SortingTypes As SortingType() = {SortingType.Ascending, SortingType.Descending}
Console.WriteLine(Data)
Console.WriteLine()
Remove some columns and rows.
Data.RemoveColumn("Threatened")
Data.RemoveRow("Quercus nigra L.")
Data.RemoveRow(2)
Console.WriteLine(Data)
Console.WriteLine()
Update a value by row and column index.
Dim RowIndex As Integer = Data.IndexOfKey("Quercus chrysolepis Liebm.")
Dim ColIndex As Integer = Data.IndexOfColumn("AcornSize")
Data(RowIndex, ColIndex) = 17.2
Get a row dictionary for one species of oak tree. The keys are the column names,
and the values are the row data.
Dim Dict As IDictionary = Data.GetRowDictionary("Quercus palustris Muenchh.")
Console.WriteLine("Quercus palustris Muenchh.")
Dim Keys As IEnumerator = Dict.Keys().GetEnumerator()
Dim Key As String
While Keys.MoveNext
Key = Keys.Current
Console.WriteLine(Key & ": " & Dict(Key))
End While
Console.WriteLine()
Get a column dictionary for the TreeHeight column. The keys are the row keys, and
values are the column data.
Dict = Data.GetColumnDictionary("TreeHeight")
Console.WriteLine("TreeHeight")
Keys = Dict.Keys().GetEnumerator()
While Keys.MoveNext
Key = Keys.Current
Console.WriteLine(Key & ": " & Dict(Key))
End While
Console.WriteLine()
Compute some descriptive statistics
Console.WriteLine("Acorn Size:")
Console.WriteLine("Mean = " & StatsFunctions.Mean(Data("AcornSize")))
Console.WriteLine("Var = " & StatsFunctions.Variance(Data("AcornSize")))
Console.WriteLine()
Export data to a DoubleMatrix. Non-numeric columns are ignored.
Dim A As DoubleMatrix = Data.ToDoubleMatrix()
Console.WriteLine(A)
Console.WriteLine()
Get a DoubleVector for the values in the AcornSize column.
Dim V As DoubleVector = Data("AcornSize").ToDoubleVector()
Console.WriteLine(V)
Console.WriteLine()
Console.WriteLine()
Console.WriteLine("Press Enter Key")
Console.Read()
End Sub
End Module
End Namespace
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