Generate random integers with probabilities

Question

I'm a bit confused about how to generate integer values with probabilities.

As an example, I have four integers with their probability values: 1|0.4, 2|0.3, 3|0.2, 4|0.1

How can I generate these four numbers taking into account their probabilities?

Answer 1

Here's a useful trick :-)

function randomWithProbability() {   var notRandomNumbers = [1, 1, 1, 1, 2, 2, 2, 3, 3, 4];   var idx = Math.floor(Math.random() * notRandomNumbers.length);   return notRandomNumbers[idx]; } 

Answer 2

A simple naive approach can be:

function getRandom(){   var num=Math.random();   if(num < 0.3) return 1;  //probability 0.3   else if(num < 0.6) return 2; // probability 0.3   else if(num < 0.9) return 3; //probability 0.3   else return 4;  //probability 0.1 }