c++ - 用 ones 和 zeros C++ 创建一个随机的 std::vector

Question

我想按我设定的比例创建一个由随机 1 和 0 组成的 vector (在我称之为 dropout 的程序中)该 vector 与之前创建的 vector CSUM 大小相同。

在 MATLAB 中会是

dropout=0.9;
n_elements=size(CSUM)
drpoutmask = (rand(n_elements) > dropout); 

在 C++ 中我有

size_t elements = Csum.size();
std::vector<float> y(elements);
std::uniform_real_distribution<float> distribution(0.0f, 1.0f); 
std::mt19937 engine; // Mersenne twister MT19937
auto generator = std::bind(distribution, engine);
std::generate_n(y.begin(), elements, generator);
std::vector<int> dropoutmask(elements,0);
float dropout=0.9;

for(int i=0; i<elements; i++)
  {
  if(y.at(i)>dropout)
    {
    dropoutmask.at(i)=1;
    }
  }
}

哪个有效，但是对于巨大的 vector 来说非常非常慢，有没有更快的方法来做到这一点？我是 C++ 的新手。

任何帮助将不胜感激

Answer 1

1. 你知道 bernoulli distribution ， 正确的？您可以使用它直接生成整数 vector 。
   示例:

   #include <iostream>
   #include <algorithm>
   #include <string>
   #include <random>
   
   int main()
   {
       constexpr double dropout = 0.9; // Chance of 0
       constexpr size_t size = 1000;
       std::random_device rd;
       std::mt19937 gen(rd());
       std::bernoulli_distribution dist(1 - dropout); // bernoulli_distribution takes chance of true n constructor
   
       std::vector<int> dropoutmask(size);
       std::generate(dropoutmask.begin(), dropoutmask.end(), [&]{ return dist(gen); });
       size_t ones = std::count(dropoutmask.begin(), dropoutmask.end(), 1);
       std::cout << "vector contains " << ones << " 1's, out of " << size << ". " << ones/double(size) << "%\n";
       std::cout << "vector contains " << size - ones << " 0's, out of " << size << ". " << (size - ones)/double(size) << "%\n";
   }
   

   实例:http://coliru.stacked-crooked.com/a/a160743185ded5c5

2. 或者，您可以创建一个所需大小的整数 vector (这会将所有元素设置为 0)，将前 N 个元素设置为 1，其中 n 是 (1 - dropout) * size(你说你想要一个比例，而不是接近比例的随机数量)然后洗牌 vector 。

   #include <iostream>
   #include <algorithm>
   #include <string>
   #include <random>
   
   int main()
   {
       constexpr double dropout = 0.9; // Chance of 0
       constexpr size_t size = 77;
       std::random_device rd;
       std::mt19937 gen(rd());
   
       std::vector<int> dropoutmask(size);
       std::fill_n(dropoutmask.begin(), dropoutmask.size() * (1 - dropout), 1);
       std::shuffle(dropoutmask.begin(), dropoutmask.end(), gen);
   
       size_t ones = std::count(dropoutmask.begin(), dropoutmask.end(), 1);
       std::cout << "vector contains " << ones << " 1's, out of " << size << ". " << ones/double(size) << "%\n";
       std::cout << "vector contains " << size - ones << " 0's, out of " << size << ". " << (size - ones)/double(size) << "%\n";
   
       for (auto i :dropoutmask) {
           std::cout << i << ' ';   
       }
       std::cout << '\n';
   }
   

实例:http://coliru.stacked-crooked.com/a/0a9dacd7629e1605