Get pseudo-random item with given probability

Question

I want to give the user a prize when he signs in; but it needs to be there some rare prizes so I want to appear prizes with different chances to appear using percents

i w

Answer 1

You can create a function to get weighted random results, something like this:

const prizes = [[50, 'flower'], [30, 'book'], [20, 'mobile']]

const total = prizes.reduce((sum, [weight]) => sum + weight, 0)

const getPrize = () => {
    const rnd = Math.random() * total
    let accumulator = 0

    for (const [weight, item] of prizes) {
        accumulator += weight

        if (rnd < accumulator) {
            return item
        }
    }
}

// check frequencies of each result

const results = {}

for (let i = 0; i < 100000; ++i) {
    const prize = getPrize()
    
    results[prize] = (results[prize] || 0) + 1
}

console.log(results)

This will work regardless of whether the weights add up to 100, whether they're integers, and so on.