weightedPick random function

[Vizcur]

I found this function really useful except for picking the last element, which is really really hard in comparison with the other elements, because only the number '1' in a random selection between  0 and 1 with double precision floating points can give the last element. Therefore, the probability of obtaining the last element is too low to be useful. 

 

var test = [0,1,2,3,4,5,6,7,8,9];for(i = 0; i< 1000000; i++){   rnd = this.game.rnd.weightedPick(test);   if(rnd == 9)       console.log(rnd);}

 

 

PS:  The way i solved this is by adding a "dummy"(or a placeholder) element in the last place of the array. So, any suggestion for a clean solution?. Thanks in advance.

[jouniii]

I was thinking this same thing, and problem lies in the weightedPick implementation of using ~~ for flooring the numbers. The solution would be either your dummy entry (workaround) or better would be to use rounding by adding + 0.5 to the algorithm.

 

Right now it is:

 

return ary[~~(Math.pow(this.frac(), 2) * (ary.length - 1))];

 

But this would result a bit better weighting:

 

return ary[~~(Math.pow(this.frac(), 2) * (ary.length - 1) + 0.5)];

[gingerbeardman]

I've also been disappointed with the results of weightedPick.

 

@jounii: I've just issued a pull request with your code suggestion, I hope that's OK?

 

https://github.com/photonstorm/phaser/pull/1751