概率实现

Question

If I have the probabilities of x, y, and z events occurring, how can I programatically realize the choosing between these three events?

Example: Pr(x) = 0.3 Pr(y) = 0.2 Pr(z) = 0.5

I'd like a function to give me a realization of these probabilities to say I should choose y, or maybe z, etc.

Any pointers or references are appreciated, thanks.

Answer 1

If you have a function rand() that returns a uniform random number in [0,1] , then

float r = rand();
if (rand < Pr(x)) {
    return x;
} else if (rand < Pr(x)+Pr(y)) {
    return y;
} else {
    return z;
}

Similarly, if you can generate a random integer between, say, 1 and 100, then

int r = rand();
if (rand < Pr(x)*100) {
    return x;
} else if (rand < (Pr(x)+Pr(y))*100) {
    return y;
} else {
    return z;
}

Answer 2

If you have probs of events, take function returning normal distrib in [0, 1) and check in which range it falls. If it in [0, 0.3) return A, if it in [0.3, 0.5) return B and otherwise return C.

Answer 3

In python you could write a program which defines a method 'chooser' which takes two parameters px and py those being the probabilties of the first two events occuring independently. The method would return x,y or z as appropriate, python code is below:

import random 

def chooser(px,py):
    prob = random.randint(1, 10)
    if (prob<=(px*10)):
        return x
    else if (prob<=((px+py)*10)):
        return y
    else:
        return z