Generate bit vector with t random ones

问题:

I want to generate an array/vector v of size p with t ones and p-t zeros. The position of the t ones must be random.

This is the solution that I've written so far, but I'm not sure if it's the most efficient one. In addition I never used random_device or mt19937 (found them here) before, so I don't know what are the possible drawbacks.

#include <algorithm>
#include <random>
#include <vector>
...
int p=10, t=3;
std::vector<int> v(p,0);
for(int i=0;i<t;i++)  //better way?
    v[i] = 1;
std::random_device rd;
std::mt19937 g(rd());
std::shuffle(std::begin(v), std::end(v), g);

This is the matlab code that I'm trying to reproduce:

rp = randperm(p);
I_s(i,:) = rp(1:t);
v = zeros(p,1);
v(I_s(i,:)) = 1;

Demo here!

回答1:

std::shuffle(std::begin(v), std::end(v), g);

Doesn't make the bit position random, it just changes the positions of the existing items (which all have the zero position bit set) in the vector randomly.

---

If I understood your requirement correctly, What you actually should have is something like:

std::random_device rd;
std::mt19937 g(rd());
for(int i=0;i<t;i++)
     v[i] = 1 << rd(); // set a random bit position