Stuipd simple calculation which I can´t slove - RE OPEN

Hello ,
I want to make a percentage calculation with Math.random
My aim is to pick one of these item by her percentage

Code:

1:40%
2:20%
3:40%

and I dont know how I can slove this q.q

so I have 40% chance to get 1 or 3 but only 20% to get 2

I add every Percentage and then I make a random nummber between 0 and the Max Percentage (100% here)

but now my problem is when 2 percentages are similar or the last percentage is the highst
would be nice if someone could help me q.q

Sorry for my bad english

 

Code:

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
 
public class WeightedGenerator<T> {
    private Map<T,Integer> table = new HashMap<T,Integer>();
    private Integer totalWeight = 0;
    public void setWeight(T key,Integer weight){
        if(weight<0) weight=0;
        totalWeight-=getWeight(key);
        table.put(key,weight);
        totalWeight+=getWeight(key);
    }
    public Integer getWeight(T key){
        if(table.containsKey(key)){
            return table.get(key);
        }else{
            return 0;
        }
    }
    public T generate(Random generator){
        T result = null;
        Iterator<T> iterator = table.keySet().iterator();
        Integer generated = generator.nextInt(totalWeight);
        while(generated>=0 && iterator.hasNext()){
            result = iterator.next();
            generated -= getWeight(result);
        }
        return result;
    }
   
}

And to use this for your particular application:

Code:

WeightedGenerator<Integer> generator = new WeightedGenerator<Integer>();
generator.setWeight(1,40);
generator.setWeight(2,20);
generator.setWeight(3,40);
generator.generate(new Random());

 

Generate your random number based on the total. Use 1 higher than the total to include 0, or shift the value up one if not.

Loop through the possible values (40, 20, 40) and add them together. When the generated number is lower use that value.

Code:

int n = new Random().nextInt(total) + 1; //100, possible n = 1 to 100
int count = 0;
for (int i : values) //40, 20, 40
{
  count += i; // count will be 40, then 60, then 100
  if (n <= count) break; // will break when n = 1 to 40 on the first value, 41 to 60 on the second, and 61 to 100 on the third
}

 

I may want to add more than this tree Items and i cant rewrite it than but thanks

Thanks this looks good an nearly than mine (so i wasen´t complet wrong *_*)
Big thanks !

 

You can use the WeightedGenerator to generate any combination you like. I was simply showing the equivalent of what you were asking for in the OP. If you had 4 items each with 25%, you'd set the weight for 1,2,3,4 all at 25. Or anything else you wanted. It is a complete general case solution.

 

Quick lesson in generics:

class WeightedGenerator<T> means T can be anything you want. T is determined when you construct the instance.

WeightedGenerator<WublyWoblyBits> generator = new WeightedGenerator<WublyWoblyBits>();
generator.setWeight(new WublyWoblyBits(7),40);
generator.setWeight(new WublyWoblyBits("herpaderp"),20);
generator.setWeight(new WublyWoblyBits(":L"),40);
WublyWoblyBits bits = generator.generate(new Random());

 

Okay thanks will keep this in my mind!

 

Hello , I use the WeightedGenerator to creat my randoms , now my problem is that when I have a double percentage wich is very low like 0.5%

Code:

Random Armor
ItemID;ArmorPack
chance;2.5%
 
Pumpkin
ItemID;86
chance;70%
 
Diamond
ItemID;264
chance;0.5%
.....

it will never take the Diamond.....
I know its because the " generated -= getWeight(result);" but don´t know how to slove this
(I want that the WeightedGenerator works with doubles like 0,05 or 0,5 ...)

Would be nice if some on could help me

Code:

    public T generate(Random generator)
    {
        T result = null;
        Iterator<T> iterator = table.keySet().iterator();
        Double generated = generator.nextDouble()*totalWeight;
        while(generated>=0 && iterator.hasNext())
        {
            result = iterator.next();
            generated -= getWeight(result);
        }
        return result;
    }

 

BUmp

 

chance al "Integer" to "Double" and "int" to "double"
double has a higer precision

 

I have :/

Code:

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Random;
 
public class WeightedGenerator<T>
{
    private Map<T,Double> table = new HashMap<T,Double>();
    private Double totalWeight = (double) 0;
   
    public void setWeight(T key,Double weight)
    {
        if(weight<0) weight=(double) 0;
       
       
        totalWeight-=getWeight(key);
        table.put(key,weight);
        totalWeight+=getWeight(key);
    }
   
    public Double getWeight(T key)
    {
        if(table.containsKey(key))
        {
            return table.get(key);
        }
        else
        {
            return (double) 0;
        }
    }
   
    public T generate(Random generator)
    {
        T result = null;
        Iterator<T> iterator = table.keySet().iterator();
        Double generated = generator.nextDouble()*totalWeight;
        while(generated>=0 && iterator.hasNext())
        {
            result = iterator.next();
            generated -= getWeight(result);
        }
        return result;
    }
   
  public int size()
  {
      return table.size();
  }
 
  public void clear()
  {
      totalWeight = (double) 0;
      table.clear();
  }
}

but when I add a while slope which only break when the result is an Item with a chance under 1% the server crashes :/

 

may I see where you implement this code, as the while statement in this code should break after there are more loops than items are

 

I allready delete this code I but I think it was:

Code:

    public T generate(Random generator)
    {
        int count = 0;
        T result = null;
    while(getWeight(result) > 1)
{
        Iterator<T> iterator = table.keySet().iterator();
        Double generated = generator.nextDouble()*totalWeight;
        while(generated>=0 && iterator.hasNext())
        {
            result = iterator.next();
            generated -= getWeight(result);
        }
count++;
}
System.out.println(count);
        return result;
    }

 

if you used the code as in the example, then it worked perfectly

 

Tested again (a with a bit changed code)

Code:

        while(true)
        {
            Double generated = generator.nextDouble()*totalWeight;
           
            while(generated>=0 && iterator1.hasNext())
            {
                result = iterator1.next();
                generated -= getWeight(result);
            }
            count++;
            result1 = result;
            if(getWeight(result1) < 1)
            {
                break;
            }
        }
        System.out.println(count + " " + result);

But it always print "2" as count (I think because it only gives 2 items) but I really don't know why :/

 

is there a reason why you can use the code that was posted earlier?

 

I have tested both same result