Random array string that doesn't repeat

[Kevin Corre]

I have a string array with 30 items in it. I would like to randomly pick 10 and have them not repeat.

Thanks,
Kevin

[Aditya Jha]

Ok.

And what have you programmed so far? Can you post some code and the output you are getting?

[Kevin Corre]

yes sorry wasn't sure if it was going to be needed. everything works it's just I get repeats when it pulls from the array.

import java.util.Random;
import java.util.Scanner;

public class Terminology
{
    
public static void main(String[] args)
{       
    String name = null;
    String input;       
    char repeat;       
      
do
{
    int count = 1; 
    do
    {
        Random generator = new Random();
        
        String[] terminology = {"gland", "joint", "life", "cancer", "heart", "head", "cerebrum", "urinary bladder",
        "cell", "skin", "electricity", "brain", "intestines", "red", "stomach", "Knowledge", "woman", "blood", "liver"};
        
        String[] answer = {"aden/o", "arthr/o", "bi/o", "carcin/o", "cardi/o", "cephal/o", "cerebr/o", "cyst/o", "cyt/o",
        "derm/o", "electr/o", "encephal/o", "enter/o", "erythr/o", "gastr/o", "gnos/o", "gynec/o", "hemat/o", "hepat/o"};
        
        int n = terminology.length;
        int r = generator.nextInt(n);
        String term = terminology[r];
        
        System.out.println("What is the combining form of " + term + "?");
        
        Scanner sc;        
        sc = new Scanner(System.in);
        name = sc.nextLine();
        
        if (answer[r].equalsIgnoreCase(name))
        {
            System.out.println("Thats right!" + "\n");            
        }
        else
        {
            System.out.println("Sorry thats wrong" + "\n" + ("The correct answer is " + answer[r] + "\n"));            
        }
        count++;
    }while (count <=10);
    
    System.out.println("Would you like to test again? " + "Enter Y for yes or N for no: ");
    
    Scanner keyboard = new Scanner(System.in);
    input = keyboard.next();
    repeat = input.charAt(0);
    
}while(repeat == 'Y' || repeat == 'y');
}
}

[Rob Spoor]

One way is to put the Strings in a List, and then remove a random element each time. Because a String will not be in the List anymore afterwards it cannot be returned by a next attempt.

[Winston Gutkowski]

Kevin Corre wrote:I have a string array with 30 items in it. I would like to randomly pick 10 and have them not repeat.

Well first off, rather than an array, you might want to consider a List (java.util.List) or a Set (java.util.Set) of Strings. You might also want to have a look at Collections.shuffle().

Winston

[John Jai]

Rob Spoor wrote:One way is to put the Strings in a List, and then remove a random element each time. Because a String will not be in the List anymore afterwards it cannot be returned by a next attempt.

Just adding that you also need to check and decrement the value of n (the upper bound) you have to create random numbers as you remove elements from the List.

[Kevin Corre]

I had looked at the collections and shuffle but not familiar with this so I wasn't sure how to implement it into the code.

[Rob Spoor]

John Jai wrote:

Rob Spoor wrote:One way is to put the Strings in a List, and then remove a random element each time. Because a String will not be in the List anymore afterwards it cannot be returned by a next attempt.

Just adding that you also need to check and decrement the value of n (the upper bound) you have to create random numbers as you remove elements from the List.

Of course. The upper bound should always be list.size(), giving you a number between 0 (inclusive) and list.size() (exclusive).

[Winston Gutkowski]

Kevin Corre wrote:I had looked at the collections and shuffle but not familiar with this so I wasn't sure how to implement it into the code.

Well if you had 30 cards and wanted to pick 10 of them at random, one way you might do it would be to shuffle the deck and deal 10 cards off the top.

Winston

[Kevin Corre]

Well I tried adding some stuff from shuffle but it still comes up with repeats. Here is the updated code. Do I have things in the wrong spot or just wrote it wrong?

import java.util.Random;
import java.util.Scanner;


public class Terminology
{
 public static void shuffleArray(String[] terminology) {
		int n = terminology.length;
		Random random = new Random();
		random.nextInt();
		for (int i = 0; i < n; i++) {
			int change = i + random.nextInt(n - i);
			swap(terminology, i, change);
		}
	}
	
	private static void swap(String[] terminology, int i, int change) {
		String helper = terminology[i];
		terminology[i] = terminology[change];
		terminology[change] = helper;
	}
	
public static void main(String[] args)
{
char repeat;
do
{
    int count = 1;
    String name = null;
    String input;
    do
    {
        Random generator = new Random();
        
        String[] terminology = {"gland", "joint", "life", "cancer", "heart", "head", "cerebrum", "urinary bladder",
        "cell", "skin", "electricity", "brain", "intestines", "red", "stomach", "Knowledge", "woman", "blood", "liver"};
        
        String[] answer = {"aden/o", "arthr/o", "bi/o", "carcin/o", "cardi/o", "cephal/o", "cerebr/o", "cyst/o", "cyt/o",
        "derm/o", "electr/o", "encephal/o", "enter/o", "erythr/o", "gastr/o", "gnos/o", "gynec/o", "hemat/o", "hepat/o"};
        
        int n = terminology.length;
        int r = generator.nextInt(n);
        String term = terminology[r];
        
        System.out.println("What is the combining form of " + term + "?");
        
        Scanner sc;
        sc = new Scanner(System.in);
        name = sc.nextLine();
        
        if (answer[r].equalsIgnoreCase(name))
        {
            System.out.println("Thats right!" + "\n");
        }
        else
        {
            System.out.println("Sorry thats wrong" + "\n" + ("The correct answer is " + answer[r] + "\n"));
        }
        count++;
        
        shuffleArray(terminology);
       
    }while (count <=10);

    System.out.println("Would you like to test again? " + "Enter Y for yes or N for no: ");
    
    Scanner keyboard = new Scanner(System.in);
    input = keyboard.next();
    repeat = input.charAt(0);
    
}while(repeat == 'Y' || repeat == 'y');
}
}

[Paul Clapham]

Yes, you "have things in the wrong spot". But regardless of the fact that your code is supposed to be doing random things, it doesn't follow that putting lines of code into random places is a good way to write that code. Don't do that. Figure out what your code is supposed to do, and in what order. Then put the lines of code in that order.

[fred rosenberger]

Kevin Corre wrote:Well I tried adding some stuff from shuffle but it still comes up with repeats. Here is the updated code. Do I have things in the wrong spot or just wrote it wrong?

Clearly if it doesn't do what you want, you wrote it wrong.

What you need to do is throw all this code away. Then sit down with pencil and paper (or the electronic equivalent), and write down IN ENGLISH how you would do this, step by step, without a computer. Then you revise that list. Then you revise it again, and again.

Only when you can look at each and every step on paper and say "oh, I know how to write that in Java" should you consider starting to write any Java. A good developer spends more time THINKKING about how/what to code than actually writing code. by a LONG chalk.

[Winston Gutkowski]

Kevin Corre wrote:Well I tried adding some stuff from shuffle but it still comes up with repeats....

By 'adding some stuff from shuffle', I assume you mean copying the code, which is the antithesis of Object-orientation.

There's nothing wrong with plagiarisim in the OO world but, to be done properly, you use the original, NOT a copy, viz:

List<String> termList = Arrays.asList(terminology);
List<String> random10 = new ArrayList<String>(10);

termList = Collections.shuffle(termList);
for (int i = 0; i < 10; i++) {
   random10.add(termList.get(i));
}

Do you see what's happened? Pure plagiarism.
Not an original thought. Not a line of code that's actually doing anything that wasn't already written (and tested) by millions of others before me.

The only original part (and believe me, the above is NOT; but it can be) is how you put it together.

Perhaps that's why they call us software engineers.

Winston

[Kevin Corre]

To Fred, no I don't need to throw away all of the code. The program was working fine before it was just repeating so I was trying to fix that. The only code I need to throw out is the code I just added and fix that.

To Winston, as I had stated in an earlier post

I had looked at the collections and shuffle but not familiar with this so I wasn't sure how to implement it into the code.

With that I was looking for some direction in how to do it and write the code because I didn't know. I had done some reading and searching and yes I had found some code that was written before by someone else and changed it to fit what I thought I needed. Sorry I didn't use the right terminology with saying "Well I added some stuff"

Kevin

[Jeff Verdegan]

Kevin Corre wrote:To Fred, no I don't need to throw away all of the code.

At the very least, you need to throw away the parallel arrays and define a class.

// wrong
String[] names = {"Joe", "Fred", "Mary"};
int[] heights = {72, 68, 66};

// better
public class Person {
  private String name;
  private int height;

  public Person(String name, int height) {
    this.name = name;
    this.height = height;
  }

  // whatever methods are needed ...
}

Person[] people = new Person[3];
people[0] = new Person("Joe", 72);
... etc.