Picking Array Values Using Probability

I have a homework to do, that is: Pick a random color, from yellow, blue and red, given the probability of: Yellow: 3/7 Blue: 1/7 Red: 3/7 I know that I could work this around by

Solution 1:

Instead of a single random value, you create as many as different items you have and later take the one with the max value.

This promotes values/items with a higher factor/probability.

Instead of this approach, you could take a single random value and take all probabilities into an array and check in which interval the random value is. Take this item.

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EDIT: The code

function getRandomIndex(probabilities) {
    var random = Math.random(),
        i;
        
    for (i = 0; i < probabilities.length; i++) {
        if (random < probabilities[i]) return i;
        random -= probabilities[i];
    }
    return probabilites.length - 1;
}

var probabilities = [3 / 7, 1 / 7, 3 / 7],
    j = 1e6,
    count = [0, 0, 0];

while (j--) count[getRandomIndex(probabilities)]++;

console.log(count);

Solution 2:

This is similar to the approach mentioned in the duplicate. You create an array with ratios same as the probabilities. (Here I'm using 2 decimal places and adding ~100 items to the array. You could add multiply by a bigger number and have .toFixed(3) for better accuracy)

function getRandomWithProbability(array) {
  const filled = array.flatMap(([color, prob]) => {
    const length = prob.toFixed(2) * 100;
    return Array.from({ length }).fill(color)
  });

  const random = Math.floor(Math.random() * filled.length);
  return filled[random]
}

const arr = [["yellow", 3/7], ["blue", 1/7], ["red", 3/7]]

console.log(getRandomWithProbability(arr))