Random.hh

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#ifndef __DIADES__UTILS__RANDOM__HH__
#define __DIADES__UTILS__RANDOM__HH__

#include<set>
#include<vector>
#include<list>

using std::set;
using std::vector;


namespace Diades
{

  namespace Utils
  {
        double generateRandomDouble(double lower, double upper);
        

        long generateRandomValue(long lower, long upper);
        
        unsigned initialiseSeed();
        
        void initialiseRandomGenerator(unsigned int seed);


        void selectNValues(unsigned int min, unsigned int max, unsigned int n, set<unsigned> & result);

        /************************************************************************************/
        
        template <typename Iterator>
        Iterator selectRandomElement(unsigned number,
                                                                 Iterator first,
                                                                 Iterator last)
        {
          if(number > 0)
                {
                  unsigned selectedIndex = generateRandomValue(0,number-1);
                  unsigned index = 0;
                  while((first != last) && (index != selectedIndex))
                        {
                          ++first;
                          ++index;
                        }
                  if(first!=last)
                        {
                          return first;
                        }
                  else
                        {
                          return last;
                        }
                }
          return last;
        }

        /************************************************************************************/
        template <typename Iterator, typename Predicate>
        Iterator selectRandomElement(Iterator first,
                                                                 Iterator last, Predicate pred)
        {
          if(first==last)
                {
                  return last;
                }
          vector<Iterator> pointers;
          for(Iterator it = first; it!=last; ++it)
                {
                  if(pred(*it))
                        {
                          pointers.push_back(it);
                        }
                }
          if(pointers.empty())
            {
              return last;
            }
          unsigned selectedIndex = generateRandomValue(0,pointers.size()-1);
          return pointers[selectedIndex];
        }

        

        /************************************************************************************/

        template <typename InputIterator, typename Predicate, typename OutputIterator>
        void selectNRandomElements(InputIterator first, InputIterator last,Predicate pred,  unsigned number,OutputIterator out)
        {
          
          if(first != last)
                {
                  vector<InputIterator> pointers;
                  for(InputIterator it = first; it!=last; ++it)
                        {
                          if(pred(*it))
                                {
                                  pointers.push_back(it);
                                }
                        }
                  if(number <= pointers.size())
                        {
                          set<unsigned> selection;
                          selectNValues(0, pointers.size() - 1, number , selection);
                          for(const unsigned & index : selection)
                                {
                                  *out = *pointers[index];
                                  ++out;
                                }
                        }
                }
        }
  };

};
#endif