VB.NET Calculating Linear Regression Slope and Intercept

• Download source code - 292.1 KB

Introduction

When it is needed to programatically calculate Linear Regression Slope and Intercept statistical values, you need to do it manually since VB.NET doesn't have many math features built in.

Program form

Background

I went looking for how to calculate linear regression slope and intercept in a program I am writing and since I have many years between me and math formulas, it was a bit of a challenge. I looked around for an example that would break down the problem into chunks for me to understand and implement into code but didn't find much.

Using the Code

Here is the basic function. The resultant variables, m and c, will contain the slope and the intercept.

To use code this as it is here:

1. Create a new "Windows Forms App (.NET Framework)" Visual Basic project in Visual Studio.
2. Add one text box to the form.
3. Set the text box to Multiline by clicking the ">" in the upper right corner and checking Multiline.
4. Make the text box bigger by dragging its edges.
5. Double click the title bar of the form to open the "FormX_load" function.
6. Paste this in and run it.

        'This is the snippet of code as shown on the codeproject page:

        'Citation: Help in understanding this formula https://www.easycalculation.com/statistics/learn-regression.php
        'This programatically mimics the behavior of the "Slope() and Intercept()" functions in MS Excel
        'This was written by Logicisme - Codeproject.org


        'Define the variables to be used:
        Dim X As New List(Of Double) 'X = First Data Set
        Dim Y As New List(Of Double) 'Y = Second Data Set
        Dim c As Double   'The intercept point of the regression line and the y axis.    
        Dim N As Integer   'Number of values or elements
        Dim ΣXY As Double 'Sum of the Product of First and Second Data Set
        Dim m As Double   'The slope of the regression line
        Dim ΣX As Double 'Sum of all of the X values
        Dim ΣY As Double 'Sum of all of the Y values
        Dim ΣX2 As Double 'ΣX2 = Sum of Square of X Data Set Values

        'Note, there is nothing special about the variables with the Σ in it. It just more closely represents the actual formula.

        'Manually adding the sample data into the two lists.
        X.Add(60)
        X.Add(61)
        X.Add(62)
        X.Add(63)
        X.Add(65)

        Y.Add(3.1)
        Y.Add(3.6)
        Y.Add(3.8)
        Y.Add(4)
        Y.Add(4.1)

        'Assign initial values into our variables.
        N = X.Count  'Adding the total number of rows of data. It really doesn't matter where this comes from so long as it matches the dataset count.
        ΣX = X.Sum 'Uses list function to add up its values
        ΣY = Y.Sum 'Uses list function to add up its values
        ΣXY = 0 'Assigning a value before first use
        ΣX2 = 0 'Assigning a value before first use

        'Calculate  ΣXY sum of the product of each row of x,y
        ' This For loop again subtracts 1 from N since N represents the count from 1 and not 0 which we need
        ' "+=" adds a value into the variable it is referencing.
        For i = 0 To N - 1
            ΣXY += X(i) * Y(i)
        Next

        'Calculate ΣX2 sum of the square of each x. This works the same way as the last loop.
        For i = 0 To N - 1
            ΣX2 += X(i) ^ 2
        Next

        'Calculate the slope. Use the cited reference for an explanation of the math
        m = ((N * ΣXY) - (ΣX * ΣY)) / ((N * ΣX2) - (ΣX ^ 2))

        'Calculate the intercept. Use the cited reference for an explanation of the math
        c = (ΣY - m * ΣX) / N


        'Puts the result text in our text box. "&=" allows you to add to the end of a text string. "vbcrlf" adds a line return
        TextBox1.Text &= "Sum of X: ΣX=" & ΣX & vbCrLf
        TextBox1.Text &= "Sum of Y: ΣY=" & ΣY & vbCrLf
        TextBox1.Text &= "Sum of the product of each row: ΣXY=" & ΣXY & vbCrLf
        TextBox1.Text &= "Rows of data n=" & N & vbCrLf
        TextBox1.Text &= "Sum of each X value squared: ΣX2=" & ΣX2 & vbCrLf

        TextBox1.Text &= "Slope: m=" & m & vbCrLf
        TextBox1.Text &= "Intercept: c=" & c & vbCrLf

The code sample in the zip contains a working program which uses a DataGridView to populate the values. It also contains a second form with this exact snippet of code.

Here is what this snippet should look like when done:

Here is what the code of the snippet looks like in Visual Studio:

Points of Interest

I used this site to get a working model of this formula going.

You will see the same dataset represented in my downloadable code so you can test the results.

I also included an Excel spreadsheet with the formulas and same data.

History

• 24^th January, 2022: Initial version
• 24th January, 2022: Applying editor suggestions