Average value of list

Question

I want to make code that will on the first click start rotorSpeed stopwatch then on the second click add rotorSpeed.ElapsedMilliseconds to list. On the second click resets stopwatch and starts timing again, then on the third click again adds rotorSpeed.ElapsedMilliseconds to list. There are no errors in the code, but when I debug it, I get an error on double average = list.Average();

Stopwatch rotorSpeed = new Stopwatch(); List<double> list = new List<double>();

private void button1_Click(object sender, EventArgs e)
{
    i++;
    //Getting rotor speed
    if (i != 2)
    {               
        if (rotorSpeed.IsRunning)
        {
            rotorSpeed.Stop();
            list.Add(rotorSpeed.ElapsedMilliseconds);
            rotorSpeed.Start();                   
        }
        else
        {
            rotorSpeed.Reset();
            rotorSpeed.Start();
        }
    }

    double average = list.Average();
    textBox2.Text = average.ToString();
}

This is the error I get:

An unhandled exception of type 'System.InvalidOperationException' occurred in >System.Core.dll

Additional information: Sequence contains no elements

That's probably because you're trying to get an `Average` of list with no elements after the first click. What's the exception you're getting? — MarcinJuraszek, Sep 24 '16 at 17:38
@pavnik An unhandled exception of type 'System.InvalidOperationException' occurred in System.Core.dll Additional information: Sequence contains no elements — rltcounter221, Sep 24 '16 at 17:39

score 23 · Answer 1 · answered Sep 24 '16 at 17:42

23

Your list is empty and so calling Average() on it throwing exception. Change the below line

double average = list.Average();

to

double average = list.Count > 0 ? list.Average() : 0.0;

answered Sep 24 '16 at 17:42

Rahul

76,197
13
71
125

6

Why `0.0`? Is it your opinion that one can silently use zero? Another option would be `list.Count > 0 ? list.Average() : double.NaN`. The average of an empty sequence can be said to be `0.0 / 0.0`, in a sense. – Jeppe Stig Nielsen Sep 24 '16 at 18:03

TigOldBitties · Answer 2 · 2016-09-24T17:56:21.663

5

if (list.Count > 0)
{
    textBox2.Text = list.Average().ToString();
}

edited Sep 24 '16 at 17:56

answered Sep 24 '16 at 17:42

TigOldBitties

1,331
9
15

count should be greater than equal to 1. – Vicky_Burnwal Sep 24 '16 at 17:47
Why? It doesn't make any sense to make an average of 1 element. LE: Unless that's what it is required to be shown in the textbox. In which case I guess you would be right :) – TigOldBitties Sep 24 '16 at 17:50
Textbox will not be populated if your list count is 1. – Vicky_Burnwal Sep 24 '16 at 17:53

score 1 · Answer 3 · edited Nov 19 '18 at 18:15

1

if (list.Count > 1)
{
    double average = list.Average();
    textBox2.Text = average.ToString();
    rotorSpeed.Stop();
}

This works just fine. Thanks!

edited Nov 19 '18 at 18:15

Alex

14,104
11
54
77

answered Sep 24 '16 at 17:57

rltcounter221

183
1
1
10

Average value of list

3 Answers3