a random number from an array

Question

I have an array

(1,2,2,2,3,3,4,5,5,5,5,5,5)

I must find randomly one position taking into account the sum of elements. for example if the 5 - is six times and the 1 - is only one, so the 5 must six times be often in random

Sorry but, your question is not clear...will you please elaborate. — Vicky, Apr 25 '12 at 10:58

Jakub Zaverka · Answer 1 · 2012-04-25T11:05:57.930

3

You need to get a random index of the array:

int randomIndex = Random.nextInt(array.length);
int randomValue = array[randomIndex]

edited Apr 25 '12 at 11:05

answered Apr 25 '12 at 10:58

Jakub Zaverka

8,816
3
32
48

2

Why Random.nextInt is better: http://stackoverflow.com/questions/738629/math-random-versus-random-nextintint :) – maksimov Apr 25 '12 at 11:01
@Jakub Zaverka (int)(Math.random() % array.length); – Nagaraju Badaeni Apr 25 '12 at 11:01
1

@nagarajub That would perform modulo on a value in range 0 - 0.9999... returning 0 every time. – Jakub Zaverka Apr 25 '12 at 11:03

score 3 · Answer 2 · answered Apr 25 '12 at 10:58

3

Something like this?

int array[] = {1,2,2,2,3,3,4,5,5,5,5,5,5};
int randomIndex = Random.nextInt(array.length);
int randomNumber = array[randomIndex];

answered Apr 25 '12 at 10:58

maksimov

5,792
1
30
38

score 1 · Answer 3 · edited May 23 '17 at 10:34

1

Like another answer said, you need an int in the range 0 : length-1.

I would advise using:

Random r = new Random();
int index = r.nextInt(array.length);
int randomValue = array[index];

Here you can see the differences between Math.random() and the nextInt() method of a Random Object:

Math.random() versus Random.nextInt(int)

edited May 23 '17 at 10:34

Community

1
1

answered Apr 25 '12 at 10:59

pcalcao

15,789
1
44
64

What, no seed? This arrangement might be dangerous if you create a new Random each time. More context is needed. – duffymo Apr 25 '12 at 11:00
duffymo: Unless you need to reproduce the results you're usually much better off not giving an explicit seed. This doesn't have anything to do with creating `Random` instances in a loop, though, which, I agree, shouldn't be done (although you can do it in Java if you can live with linearly correlated seeds). – Joey Apr 25 '12 at 11:06

score 0 · Answer 4 · answered Apr 25 '12 at 11:07

try this:

  1 import java.util.Random;
  2 
  3 class Rnd {public static void main(String... args) {
  4     int[] data = new int[]{1,2,2,2,3,3,4,5,5,5,5,5,5};
  5     System.out.print(data[new Random().nextInt(data.length)]);
  6  }
  7 }

nextInt() method "Returns a pseudorandom, uniformly distributed int value between 0 (inclusive) and the specified value (exclusive), drawn from this random number generator's sequence.". Because random is uniformly distributed, you'll get your number as more often, as more often it includes in an array.

a random number from an array

4 Answers4