discrete distribution

[raefnal]

I'm familiar with discrete and weighted distributions,I just
can't seem to figure out how to do what I need...
I need to be able to pick a random item from a vector with eqch
item having a different probability of being chosen. Also, I'm looking to manually fill the vector with specific items. I can't seem to figure
this out or find the appropriate code
Any help is welcome

[Peter87]

Not sure which part you're having problem with but here is an example using std::discrete_distribution.

#include <iostream>
#include <random>

int main()
{
	std::vector<std::string> items =    {"screwdriver", "door", "house", "pizza"};
	std::vector<double> probabilities = { 10,            20,     50,      20};
	
	std::mt19937 rng(std::random_device{}());
	std::discrete_distribution<> dist(probabilities.begin(), probabilities.end());
	
	int random_item_index = dist(rng);
	const std::string& random_item = items[random_item_index];
	std::cout << "Random item: " << random_item << "\n";
}

[raefnal]

That looks like it may do what I need...thank you. I'll try it tonight and report back.

[raefnal]

Is there a way to set it up to run more than once and to eliminate previous choices as possible future choices?

[Ganado]

A 'while' loop, and remove the eliminated element from the vector and re-initialize the dist every time in the loop.
You shouldn't need to re-initialize the rng each loop iteration. That can happen once, at the beginning before the loop.

[raefnal]

Perfect. Thank you.

[raefnal]

Okay...the code Peter87 shared works, but it always chooses the last item in the vector no matter how the probability is distributed. Any ideas?

[mbozzi]

What is your compiler? What is your standard library? Exact version numbers please.

Some obsolete implementations don't completely implement the stuff in <random>. For example std::random_device might be pseudorandom (if I remember correctly) in some versions of libstdc++.

[Peter87]

Yeah, std::random_device was broken in some old versions of MinGW.

You might want to use the current time as seed instead.

std::mt19937 rng(std::time(nullptr));