(C++) std::random_shuffle

Function to shuffle an array or vector. Can be found in the STL header file algorithm.h.

include <iostream>

include <vector>

include <algorithm>


int main()
{
  const int size = 5;
  std::vector<int> myVector(size);
  for (int i=0; i!=size; ++i) myVector[i]=i;
  std::cout << "Vector before shuffling: " << std::endl;
  for (int i=0; i!=size; ++i) std::cout << i << " : " << myVector[i] << std::endl;
  std::random_shuffle(myVector.begin(), myVector.end());
  std::cout << "Vector after shuffling: " << std::endl;
  for (int i=0; i!=size; ++i) std::cout << i << " : " << myVector[i] << std::endl;
}

Testing std::random_shuffle

How random does std::random_shuffle shuffle? Here is a test giving the impression it does a pretty nice job, although I does not include any statistics.

include <iostream>

include <vector>

include <algorithm>

include <numeric>


std::vector<double> getInitVector(const int& size)
{
  std::vector<double> v(size);
  for (int i=0; i<size; ++i) v[i] = i;
  return v;
}
int main()
{
  const int size = 100;
  const int nTests = 10000;
  const std::vector<double> vOrig = getInitVector(size);
  const double average = std::accumulate(vOrig.begin(),vOrig.end(),0.0) / static_cast<double>(size);
  //Start the tests
  std::vector<double> sums(size,0.0);
  for (int i=0; i<nTests; ++i)
  {
    std::vector<double> vCopy(vOrig);
    std::random_shuffle(vCopy.begin(), vCopy.end());
    for (int j=0; j<size; ++j)
    {
      sums[j] += vCopy[j];
    }
  }
  std::cout << "Expected value: " << average * nTests << std::endl;
  for (int i=0; i!=size; ++i)
  {
    std::cout << i << " : " << sums[i] << std::endl;
  }
}

Code links

last edited (November 16, 2006) by bilderbikkel, Number of views: 2693, Current Rev: 5 (Diff)

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