Suppose there is an array :
int arr[] = {0,1,2}
Is there a way I can generate a random number out of 0,1,2 (i.e from the array) ?
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you mean pick randomy one of these numbers witch the array is holding ?A4L– A4L2013-04-04 12:07:49 +00:00Commented Apr 4, 2013 at 12:07
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@A4L yeah I mean the samesaplingPro– saplingPro2013-04-04 12:10:23 +00:00Commented Apr 4, 2013 at 12:10
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QuadroQ explains how, Sano shows how.A4L– A4L2013-04-04 12:12:32 +00:00Commented Apr 4, 2013 at 12:12
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4 Answers
try this
import java.util.Random;
Random random = new Random();
System.out.println(arr[random.nextInt(arr.length)]);
Comments
Sure. You should generate a number between 0 and arr.length-1, round it to a int number and then take the arr[your_random_number] element.
int random_index = (int) round(Math.random() * (arr.length - 1));
then your element would be arr[random_index]
4 Comments
Matei Suica
what do you mean by repeated?
Jacob is on Codidact
This is random, but not fair, as the rounding causes
0 and arr.length - 1 to both occur roughly half as often as any other number. Better to use aRandom.nextInt(arr.length) or (int) (Math.random() * arr.length)Matei Suica
yeah, might be ... i'm not really that familiar with the statistical problems random might have.
Thorn
The standard way to do this is (int) (Math.random()*arr.length) - this gives us exactly what we want with equal probability.
If you want unique element each time from the array then try this:
Integer arr[] = {0,1,2}
Collections.shuffle(Arrays.asList(arr));
for(int unique: ar)
System.out.println(unique);
Shuffle method of Collections will randomly shuffle the given array .
7 Comments
jlordo
this won't work as you expect for a
int[], only for a Integer[]. With arr being int[] this Arrays.asList(arr) will return a list of length 1, which makes no sense shuffling...
Achintya Jha
@jlordo Using Random can generate same number more than once...yes?
A4L
this is not what the questioner wants, this will alter the list placing each element randomly somewhere else.
jlordo
@A4L: No, it is no placing each element somewhere else, it does nothing, because
arr is a int[]. I'll post some code in a minute.jlordo
Look at this http://ideone.com/kCK0TE for
int[] and this http://ideone.com/u8tjnZ for Integer[]. and see the difference. |
This will pick a number randomly out of the array.
public static void main(String[] args)
{
int arr[] = {0,1,2};
System.out.println(arr[(int)(Math.random()*arr.length)]);
}
