How can I find the average of all numbers in a textfile - vb.net

Question

I'm ridiculously stuck on this one. My code below sums up all the numbers that are in the textfile Dailyfile and outputs the total to AverageFile. The problem is I don't want it to sum up. I want it to find out the average of all the numbers.
How can I do this?
Dim AverageFile As String = "C:\xxx\zzz\" & System.DateTime.Now.ToString("yyyyMMdd") & ".txt"
Dim DailyFile As String = "C:\xxx\xxx\" & System.DateTime.Now.ToString("yyyyMMdd") & ".txt"
Try
If System.IO.File.Exists(AverageFile) Then
Dim total As double = 0
For Each line As String In IO.File.ReadAllLines(DailyFile)
total += Double.Parse(line)
Next
Dim objWriter As New System.IO.StreamWriter(AverageFile, false)
objWriter.WriteLine(total.ToString)
objWriter.Close()
Else
'Nothing yet
End If
Catch ex As Exception
lbErrors.Items.Add(String.Concat(TimeOfDay & " Error 98: File or folder might not exist. Restart application... ", ex.Message))
End Try
The Dailyfile simply looks like this;
I've tried a bunch of variations on the total 0= double.parse(line), because I feel like thats where the problem lies. I've also tried diming the total as integer = 0. I'm new to the calculating, so I don't know how things go.

Answer 1

The average is just the total divided by the number of things you summed up. (Assuming you want to use the arithmetic mean, which is probably what you are looking for.)
Dim total As double = 0
Dim numOfLines As Integer = 0
For Each line As String In IO.File.ReadAllLines(DailyFile)
numOfLines += 1
total += Double.Parse(line)
Next
Dim average As Double = total / numOfLines
Dim objWriter As New System.IO.StreamWriter(AverageFile, false)
objWriter.WriteLine(average.ToString)
objWriter.Close()
What was missing in your code is just keeping track of the number of lines and dividing the sum by this number.
Just as an example: We are 3 people. I am 23 years old, you are 35 years old, our friend is 40 years old. The average of our ages would be (23 + 35 + 40) / 3 which is 32.666...

Answer 2

Either use CherryDT's approach to count the lines and divide the total through this number or use LINQ's Enumerable.Average, for example with this concise query:
Dim allNumbers = From line In IO.File.ReadLines(DailyFile)
Let num = line.TryGetDouble()
Where num.HasValue
Select num.Value
Dim average As Double = allNumbers.Average()
I've used following extension method to try-parse the string to a Nullable(Of Double):
Imports System.Runtime.CompilerServices
Module StringExtensions
<Extension()>
Public Function TryGetDouble(ByVal str As String) As Nullable(Of Double)
If str Is Nothing Then Return Nothing
Dim d As Double
If Double.TryParse(str.Trim(), d) Then
Return d
Else
Return Nothing
End If
End Function
End Module