Question

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Count Frequency in a Randomly Generated List of Numbers

I am currently working with arrays and random numbers. I have a created a form that will let me generate random numbers from 1 – 20 with a textbox1 to choose the quantity of numbers displayed. I am displaying the results inside a multiline textbox2. I have been able to calculate the sum and average of the set of numbers generated.

My second step:

Is there away to tally or mark the times a number is generated and display it in the multiline textbox(last picture)? Would I need to create an array and make it full of zero?

private void button1_Click(object sender, EventArgs e)
{
    int n = Convert.ToInt32(textBox1.Text);
    int[] y = new int[n];
    double sum = 0;

    for (int i = 0; i < n; i++)
    {
        int x = 1 + r.Next(20);
        y[i] = x;
        sum += x;

        if (n < 101)
            textBox2.AppendText(x + " ");
    }

    double avg = sum / n;
    textBox2.AppendText(Environment.NewLine + sum + " " + avg + Environment.NewLine);

    double vsum = 0;

    for (int i = 0; i < n; i++)
        vsum += (y[i] - avg) * (y[i] - avg);
}     

Form.cs

Count the times an integer is randomly selected

Answer 1

Here’s the code that can do what you want:

        var r = new Random();
        var n = int.Parse(this.textBox1.Text);

        var y =
            Enumerable
                .Range(0, n)
                .Select(x => r.Next(20) + 1)
                .ToArray();

        var sum = y.Sum();
        var avg = (double)sum / (double)n;
        var frequency = y.ToLookup(x => x);

        textBox2.Text = String.Join(Environment.NewLine, new[]
        {
            "Results",
            String.Format("{0} {1}", sum, avg),
        }.Concat(Enumerable
            .Range(1, 20)
            .Select(x => String.Format("{0} ({1}x)", x, frequency[x].Count()))));

Running this with a value of 25 I got this result:

Results
278 11.12
1 (0x)
2 (2x)
3 (1x)
4 (1x)
5 (1x)
6 (2x)
7 (0x)
8 (1x)
9 (2x)
10 (4x)
11 (1x)
12 (0x)
13 (0x)
14 (0x)
15 (2x)
16 (1x)
17 (2x)
18 (2x)
19 (3x)
20 (0x)

Is that what you’re after?