randomSampleSelector.h

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#ifndef DLR_COMPUTERVISION_RANDOMSAMPLESELECTOR_H
#define DLR_COMPUTERVISION_RANDOMSAMPLESELECTOR_H

#include <vector>
#include <dlrRandom/pseudoRandom.h>

namespace dlr {

  namespace computerVision {

    template <class Sample>
    class RandomSampleSelector {
    public:

      // ========= Public typedefs. =========

      typedef Sample SampleType;

      typedef std::pair<typename std::vector<SampleType>::const_iterator,
                        typename std::vector<SampleType>::const_iterator>
        SampleSequenceType;


      // ========= Public member functions. =========

      template <class IterType>
      RandomSampleSelector(IterType beginIter, IterType endIter)
        : m_sampleVector(beginIter, endIter) {}


      SampleSequenceType
      getPool() {
        return std::make_pair(m_sampleVector.begin(), m_sampleVector.end());
      }


      size_t
      getPoolSize() {return m_sampleVector.size();}


      SampleSequenceType
      getRandomSample(size_t sampleSize);


      template<class IterType>
      SampleSequenceType
      getSubset(IterType beginIter, IterType endIter);
      
    private:
      
      dlr::random::PseudoRandom m_pseudoRandom;
      std::vector<SampleType> m_sampleVector;

    };

  } // namespace computerVision
  
} // namespace dlr


/* ============ Definitions of inline & template functions ============ */


namespace dlr {

  namespace computerVision {

    template <class Sample>
    typename RandomSampleSelector<Sample>::SampleSequenceType
    RandomSampleSelector<Sample>::
    getRandomSample(size_t sampleSize)
    {
      for(size_t ii = 0; ii < sampleSize; ++ii) {
        int jj = m_pseudoRandom.uniformInt(ii, m_sampleVector.size());
        std::swap(m_sampleVector[ii], m_sampleVector[jj]);
      }
      return std::make_pair(
        m_sampleVector.begin(), m_sampleVector.begin() + sampleSize);
    }

    
    template <class Sample>
    template<class IterType>
    typename RandomSampleSelector<Sample>::SampleSequenceType
    RandomSampleSelector<Sample>::
    getSubset(IterType beginIter, IterType endIter)
    {
      typedef typename std::vector<SampleType>::iterator SampleIter;

      SampleIter poolIter = m_sampleVector.begin();
      SampleIter candidateIter = m_sampleVector.begin();
      while(beginIter != endIter && candidateIter != m_sampleVector.end()) {
        if(*beginIter) {
          if(candidateIter != poolIter) {
            std::swap(*poolIter, *candidateIter);
          }
          ++poolIter;
        }
        ++beginIter;
        ++candidateIter;
      }
      return std::make_pair(m_sampleVector.begin(), poolIter);
    }

    
  } // namespace computerVision
  
} // namespace dlr

#endif /* #ifndef DLR_COMPUTERVISION_RANDOMSAMPLESELECTOR_H */