Randomly pick from a vector in C++? - c++

Question

I have a vector that allows for duplicates, I want to randomly chose an element with the probability that represents how many times an element was repeated.
For example - for the vector below, 6 should have the highest probability of being chosen. I thought about using rand(), but I am not quiet sure how to incorporate the probability.
vector A = [ 0, 0, 2, 2, 4, 5, 1, 6, 6, 6]
thanks

Answer 1

I think you are on the right way for getting a custom distribution of values. See the following code which demonstrates the access to the vector. Hope it helps.
#include <cstdlib>
#include <iostream>
#include <ctime>
#include <vector>
int main()
{
std::vector<int> A { 0, 0, 2, 2, 4, 5, 1, 6, 6, 6 };
std::srand(std::time(0)); // use current time as seed for random generator
int random_pos = std::rand() % A.size(); // Modulo to restrict the number of random values to be at most A.size()-1
int random_val = A[random_pos];
}

Answer 2

Maybe something like this (untested!):
#include <vector>
#include <random>
#include <iostream>
int main()
{
std::vector<size_t> A{0, 0, 2, 2, 4, 5, 1, 6, 6, 6};
static thread_local std::mt19937 g{std::random_device{}()};
static thread_local std::uniform_int_distribution<size_t> d{0,A.size()};
std::cout << A[d(g)] << std::endl;
}