how select randomly from an int array, then remove the selected element

Question

im trying to select randomly from an array to print it, then remove it from the array, to avoid printing out the same number twice. i am a bit of a java novice so was wondering if someone could point me where im going wrong.

public static void main(String[] args) {
    int[] colm = { 1, 2, 3, 4, 5, 67, 87 };
    Random rand = new Random();

    for (int i = 0; i < 5; i++)
        System.out.println(" " + colm[rand.nextInt(colm.length)]);

}

thanks

You don't want to print the same number twice,hence everytime you'll have to decrease the range of Random number created — Kraken
– Kraken, Commented Apr 4, 2014 at 9:55
Also, you are not removing the number from Array after you've picked it. You are just printing it on the console. — Kraken
– Kraken, Commented Apr 4, 2014 at 9:57
And since we don't live in caves, we don't wear human skins, please don't use Array. Cheers — Kraken
– Kraken, Commented Apr 4, 2014 at 9:58

stinepike · Accepted Answer · 2014-04-04 09:56:45Z

5

Random doesn't give gurranty of unique number. you can do following instead.

public static void main(String[] args) {
    int[] colm = { 1, 2, 3, 4, 5, 67, 87 };
    List l = new ArrayList();
    for(int i: colm)
        l.add(i);

    Collections.shuffle(l);

    for (int i = 0; i < 5; i++)
        System.out.println(l.get(i));

}

answered Apr 4, 2014 at 9:56

stinepike

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3 Comments

Gabrer Over a year ago

More elegant than others, but you didn't remove elements. Am I right?

stinepike Over a year ago

@Gabrer. yes I didn't remove that. Because although the title asked to remove from array but the main goal of OP was to avoid printing duplicate entries.

Gabrer Over a year ago

Ok! I understand. But actually, I chose this answer on Google because in the title there was the "remove". It's up to you if improve the answer (anyway, it needs only to call the "remove()" method).

enterbios · Accepted Answer · 2014-04-04 10:21:29Z

3

You are missing the remove part. Try something like this:

public static void main(String[] args)
{
    Integer [] colm = {1,2,3,4,5,67,87};
    final List<Integer> ints = new ArrayList<Integer>(Arrays.asList(colm));
    Random rand =  new Random();

    for(int i = 0; (i<5) && (ints.size() > 0); i ++) {
        final int randomIndex = rand.nextInt(ints.size());
        System.out.println(" " +  ints.get(randomIndex));
        ints.remove(randomIndex);
    }
}

edited Apr 4, 2014 at 10:21

answered Apr 4, 2014 at 9:54

enterbios

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2 Comments

Arjit Over a year ago

it will throw exception if you are using list as final.

enterbios Over a year ago

The exception was not due to final, Arrays.asList(colm) creates fixed size List which do not support removing, fixed that :)

Sanjay Rabari · Accepted Answer · 2014-04-04 09:53:33Z

0

You better use Set or Map to hold the data and then create random number which belongs in the length of the set/map and remove with that (random) index.

answered Apr 4, 2014 at 9:53

Sanjay Rabari

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2 Comments

JB Nizet Over a year ago

Set and Map don't have indices. A List would be more appropriate.

Lukas Warsitz Over a year ago

Also maybe the OP does this for exercise, so it would be great to give him an answer for his code.

Harleen · Accepted Answer · 2020-09-08 19:59:15Z

public static void removeElements(int[] arr) {
        Random random = new Random();

        List<Integer> list = Arrays.stream(arr).boxed().collect(Collectors.toList());

        int length = arr.length;
        while (length > 0) {

            System.out.println("Size: " + list.size());
            if (list.size() == 1) {
                int randomIndex = random.nextInt(list.size());
                list.remove(randomIndex);
                System.out.println("Size:--> " + list.size());
                break;
            }else {
                int randomIndex = random.nextInt(list.size() - 1);
                if (arr == null || randomIndex > arr.length) {
                    System.out.println("No Elements to be deleted");
                }
                list.remove(randomIndex);
                System.out.println("Removed Element: " + list.get(randomIndex));
                length--;

                if (length == 0)
                    break;

            }
        }

    }

toolic · Accepted Answer · 2023-04-05 12:08:22Z

0

public static void main(String[] args) {
int[] colm = { 1, 2, 3, 4, 5, 67, 87 };
List l = new ArrayList();
for(int i: colm)
    l.add(i);

Collections.shuffle(l);

for (int i = 0; i < 5; i++)
    System.out.println(l.get(i));

}

edited Apr 5, 2023 at 12:08

toolic

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answered Apr 5, 2023 at 11:47

Jan Phillip Dacallos

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