How do I take one item randomly from a list then prevent its repeatition?

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I have a list like this:

C#

List<string> numbers = new List<string>();
            numbers.Add("1");
            numbers.Add("2");
            numbers.Add("3");
            numbers.Add("4");
            numbers.Add("5");
            numbers.Add("6");
            numbers.Add("7");
            numbers.Add("8");
            numbers.Add("9");
            numbers.Add("10");
            numbers.Add("11");
            numbers.Add("12");
            numbers.Add("13");
            numbers.Add("14");
            numbers.Add("15");
            numbers.Add("16");
            numbers.Add("17");
            numbers.Add("18");
            numbers.Add("19");
            numbers.Add("20");
            numbers.Add("21");
            numbers.Add("22");
            numbers.Add("23");
            numbers.Add("24");
            numbers.Add("25");
            numbers.Add("26");
            numbers.Add("27");
            numbers.Add("28");
            numbers.Add("29");
            numbers.Add("30");
            numbers.Add("31");
            numbers.Add("32");
            numbers.Add("33");
            numbers.Add("34");
            numbers.Add("35");

Now I want to achieve 3 tasks:
1: take one of the members randomly.
2: prevent the shown number to repeat
3: being able to restart the list.(like resetting the list so any number can come again but still repeated ONCE)
Thanks in advance for all your help...

Posted 4-May-15 21:49pm

Helifiction

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Santosh K. Tripathi 5-May-15 4:14am

what you have tried till now?

2 solutions

Solution 2

I would generate a random sequence and store it in a list:

C#

var rnd = new Random();
var list = Enumerable.Range(1, 35)
	.Select(x => new {Value = x, SortKey = rnd.Next()})
	.OrderBy(x => x.SortKey)
	.Select(x => x.Value)
	.ToList();

Then you can easily select number one by one. If you which to reset then you just simply move the pointer to the first element. Alternatively you can generate a new list.

Posted 4-May-15 22:42pm

Tomas Takac

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OriginalGriff · Accepted Answer · 2015-05-04T22:15:00

Solution 1

First off, you don't have to specify the number individually:

C#

List<string> numbers = Enumerable.Range(1, 28).Select(i => i.ToString()).ToList();

Will fill it nicely.
And you can create a copy of the list for later "reset" very easily:

C#

List<string> original = numbers.ToList();

Get one randomly? Also simple:

C#

private Random rand = new Random();
...
    int index = rand.Next(numbers.Count);
    string value = numbers[index];

And to prevent repetition, just add one line:

C#

numbers.RemoveAt(index);

[edit]Stupid HTML tag autocomplete...[/edit]

Posted 4-May-15 22:15pm

OriginalGriff

Updated 4-May-15 22:16pm

v2

Comments

CPallini 5-May-15 4:35am

5

Helifiction 5-May-15 4:42am

thanks a million times but how do I display it in a text box?
I have a textbox that I want the number on it but when I try:
private void pickWinner_Click(object sender, EventArgs e)
{ Random rand = new Random();
int index = rand.Next(numbers.Count);
string value = numbers[index];
numbers.RemoveAt(index);
textBox1.Text = (numbers[rand.Next(0, 40)])
}
I get a out of the range exception.
Thanks again

OriginalGriff 5-May-15 5:03am

What did you expect? You just deleted it!

That was why I saved the value in "value" *before* I removed it...

Helifiction 5-May-15 5:06am

Wow ok now I got it thanks hundreds of times for you answers. :)

OriginalGriff 5-May-15 5:12am

You're welcome!

BillWoodruff 5-May-15 5:11am

+5 Oh, yeah.

Helifiction 5-May-15 5:29am

So sorry @originalGriff butt I have another question: when I closed the app it reset it self how do I prevent that.(I mean even though it had been closed but when restarted retrieve the previous session.) thanks...

OriginalGriff 5-May-15 5:43am

You'd have to store the info somewhere are reload it when you started - that's rather more complex!
What have you tried? What storage do you know?
Are you familiar with files, Settings files, and so forth?

OriginalGriff 5-May-15 5:43am

And what environment are you working in?