Way to refer back to an old random instance when a new one is already made?

Question

So my general question is: is there a way to refer to an old random instance after declaring a new one?

First, the following is the code that I'm currently using.

This is the list I created:

        Random p1rnd = new Random();
        List<string> p1list = new List<string>();
        p1list.Add("A");
        p1list.Add("B");
        p1list.Add("C");
        p1list.Add("D");
        p1list.Add("E");
        p1list.Add("F");
        p1list.Add("G");
        p1list.Add("H");
        p1list.Add("I");
        p1list.Add("J");
        int p1r = p1rnd.Next(p1list.Count);

This is the block of code where I used the list, and is what I'm currently having an issue with:

Console.WriteLine("\nWhat would you like to say?");
                    Console.Write("A. ");
                    p1r = p1rnd.Next(p1list.Count); //CHOICE A
                    Console.Write(p1list[p1r]);
                    Console.Write("B. ");
                    p1r = p1rnd.Next(p1list.Count); //CHOICE B
                    Console.Write(p1list[p1r]);
                    Console.Write("C. ");
                    p1r = p1rnd.Next(p1list.Count); //CHOICE C
                    Console.Write(p1list[p1r]);
                    p1choiceA = Console.ReadLine();

Basically, I'm planning to use if-else statements to remove the choices. However, I don't know how to phrase my condition.

        if ( ) // SHOULD BE CHOICE A
        {
        p1list.Remove( )
        }
        else if ( ) // SHOULD BE CHOICE B
        {
        p1list.Remove( )
        }
        else if ( ) // SHOULD BE CHOICE C
        {
        p1list.Remove( )
        }

Typically, I would use p1list[p1r]. But, given that I created new random instances for each, I don't know what to put anymore. How would I refer to the instance used in CHOICE A and B? Thanks.

Answer 1

If I understand your requirements correctly, you wish to show three random choices. The user gets to pick one, which gets removed from the list. Then he gets to see three more choices: the two remaining from the original list, plus an additional random one. Is that correct?

My suggestion:

First, sort your list into a random order. This makes everything else way easier.

//using System.Linq;
var sortedList = p1list.OrderBy( s => p1rnd.NextDouble() ).ToList();

Now that the list is sorted, it is very simple to select three questions. Just pick the first three!! And if you ever need to know which ones you picked... they were the first three. This satisfies the requirements of both randomness and recall.

To compose a list for display to the user, Zip() the list with an array containing the choice identifiers (the letters A, B, and C).

    var choiceLetters = new [] { "A", "B", "C" };

    var choiceStrings = choiceLetters.Zip
    (
        sortedList, 
        (a,b) => string.Format("{0}. {1}", a, b)
    );
    Console.WriteLine("What would you like to say?");
    foreach (var s in choiceStrings) 
    {
        Console.WriteLine(s);
    }

To remove one, just remove it from the sortedList.

    var choiceLetter = Console.ReadLine();
    var choiceIndex = Array.IndexOf(choiceLetters, choiceLetter.ToUpper());
    if (choiceIndex == -1) break;  //User didn't pick A, B, or C

    sortedList.RemoveAt(choiceIndex);

Complete solution:

public static void Main()
{
    Random p1rnd = new Random();
    List<string> p1list = new List<string>
    {
        "These sentences make up the random list of choices.",
        "In your example you used single letters.",
        "That was kind of confusing.",
        "The user always sees A, B, and C.",
        "But not sentences 0, 1, and 2.",
        "I'll have a beer please."
    };

    var sortedList = p1list.OrderBy( s => p1rnd.NextDouble() ).ToList();

    var choiceLetters = new [] { "A", "B", "C" };

    while (true)
    {
        var choiceStrings = choiceLetters.Zip
        (
            sortedList, 
            (a,b) => string.Format("{0}. {1}", a, b)
        );

        Console.WriteLine("What would you like to say?");
        foreach (var s in choiceStrings) 
        {
            Console.WriteLine(s);
        }

        var choiceLetter = Console.ReadLine();
        var choiceIndex = Array.IndexOf(choiceLetters, choiceLetter.ToUpper());
        if (choiceIndex == -1) break;  //User didn't pick A, B, or C

        sortedList.RemoveAt(choiceIndex);
    }
}