VB.NET Normalizing Data [1, -1]

Question

I am currently using the following code to normalize data:

Public Function NormalizeData(values As Double()) As Double()
    Dim min = values.Min
    Dim max = values.Max
    Dim outList(values.Count - 1) As Double
    For i = 0 To values.Count - 1
        outList(i) = (values(i) - min) / (max - min)
    Next
    Return outList
End Function

This returns values from 0 to 1 accordingly. I am confused on how to make this normalize between [1, -1] instead of [1, 0].

Answer 1

You already know how to normalise to a range of 0 to 1. If you want the range to be -1 to 1, you just need to multiply the normalised data by 2 and subtract 1.

As I said in my comment, you could just modify the statement inside your For loop to adjust the data:

outList(i) = 2 * (values(i) - min) / (max - min) - 1

The equivalent statement to denormalise data would be:

outList(i)= (values(i) + 1) * (max - min) / 2 + min

If you need to normalise and denormalise several arrays of data, I suggest creating a NormalData class that can store the normalised data as well as the maximum and minimum values and has properties that will return either the normalised or denormalised values. Here is an example of such a class. You can create it using either

• An array of unnormalised data, or ...
• An array of normalised data and the minimum and maximum values

The NormalValues and Values properties return the normalised and denormalised data respectively.

Public Class NormalData
    ''' <summary>Create a NormalData object from and unnormalised array of values</summary>
    ''' <param name="values">Unnormalised values</param>
    Sub New(values() As Double)
        Minimum = values.Min
        Maximum = values.Max
        NormalValues = values.Select(Function(val) 2 * (val - Minimum) / (Maximum - Minimum) - 1).ToArray
    End Sub

    ''' <summary>Create a NormalData object from and normalised array of values</summary>
    ''' <param name="normal">Normalised values</param>
    ''' <param name="min">Minimum value of unnormalised data</param>
    ''' <param name="max">Maximum value of unnormalised data</param>
    Sub New(normal() As Double, min As Double, max As Double)
        Minimum = min
        Maximum = max
        NormalValues = normal
    End Sub

    ReadOnly Property Minimum As Double
    ReadOnly Property Maximum As Double

    ReadOnly Property NormalValues As Double()

    ReadOnly Property Values As Double()
        Get
            Return NormalValues.Select(Function(norm) (norm + 1) * (Maximum - Minimum) / 2 + Minimum).ToArray
        End Get
    End Property
End Class