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weightedPick random function

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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 =;   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.

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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)];

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