How do i get the Average, Highest and Lowest of values from a listbox and then display it on a textbox

Question

I have the following code, how can I get the values from the items in the listbox and get my program to find the average, highest and lowest of the values. I currently have the following textboxes (averageTextbox, highestTextbox, lowestTextbox) and I wish to display the values accordingly into the textboxes. Thanks in Advance!

private void readButton_Click(object sender, EventArgs e)
{
    int counter = 0;
    string line;
    System.IO.StreamReader file = new System.IO.StreamReader(
        @"C:\Users\Harra\Documents\Visual Studio 2017\Projects\File Reader\Sales.txt");
    double dblAdd = 0;

    while ((line = file.ReadLine()) != null)
    {
        displayListBox.Items.Add(line);
        dblAdd += Convert.ToDouble(line);
        counter++;
    }

    totalTextBox.Text = string.Format("{0:F}", dblAdd);
}

You're getting the double values in `Convert.ToDouble(line)` on each iteration. Do the calculations in the loop. All you're doing is calculating a sum, but you could easily assign that converted double to a local variable and do any number of things with it. — 15ee8f99-57ff-4f92-890c-b56153, May 18 '17 at 18:39
Hi, I wish to keep the sum calculation. I didn't quite understand what you were saying? sorry, I'm really new to programming — Relaxsingh, May 18 '17 at 18:46
See answer. You should be able to figure out everything it's doing, as it's very basic, but feel free to ask if you have any questions. — 15ee8f99-57ff-4f92-890c-b56153, May 18 '17 at 18:50
HI, thanks for your answer. How would I display the Highest, lowest and average value to the appropriate textbox? my textboxes are called: highestTextbox, lowestTextbox and averageTextbox. Thanks again — Relaxsingh, May 18 '17 at 19:14
You figured out how to put a value in `totalTextbox`, didn't you? Do it the same way for the others. — 15ee8f99-57ff-4f92-890c-b56153, May 18 '17 at 19:15

Rufus L · Answer 1 · 2017-05-18T20:41:29.430

1

Ed's answer is most likely the way to go, but here's another way you can do it (from any code that has access to your displayListBox).

Note that this only works after the ListBox has been populated with doubles. It also requires a reference to System.Linq, which provides extension methods that we make use of (Cast, Sum, Max, Min, and Average):

using System.Linq;

The following line will take all the ListBoxItems, cast them to strings, then convert them to doubles:

IEnumerable<double> listBoxDoubleItems = 
    displayListBox.Items.Cast<string>().Select(Convert.ToDouble);

Now that you have an IEnumerable<double> to work with, you can use the Linq extension methods to get what you're looking for:

double total = listBoxDoubleItems.Sum();
double highest = listBoxDoubleItems.Max();
double lowest = listBoxDoubleItems.Min();
double average = listBoxDoubleItems.Average();

edited May 18 '17 at 20:41

answered May 18 '17 at 19:01

Rufus L

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Some days I shouldn't even get out of bed. This is much better than my answer. – 15ee8f99-57ff-4f92-890c-b56153 May 18 '17 at 19:15
1

Might want to mention he needs to be using the name space System.Linq. I much prefer this over the other answer as it is much cleaner. But by chance the asker is using an old version of .NET that doesn't have linq the other answer will do. – Dan P May 18 '17 at 19:24
Thanks for your help! – Relaxsingh May 18 '17 at 19:46

score 0 · Accepted Answer · answered May 18 '17 at 18:49

double lowest = Double.MaxValue;
double highest = Double.MinValue;
double average = 0;

while ((line = file.ReadLine()) != null)
{
    displayListBox.Items.Add(line);

    var dbl = Convert.ToDouble(line);

    if (dbl > highest)
        highest = dbl;

    if (dbl < lowest)
        lowest = dbl;

    dblAdd += dbl;

    counter++;
}

if (counter > 0)
{
    average = dblAdd / (double)counter;
}
else
{
    highest = lowest = 0;
}

You already know how create a TextBox, and how to format a double and display it in a TextBox.

How do i get the Average, Highest and Lowest of values from a listbox and then display it on a textbox

2 Answers2