THistView.hxx

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/// \file ROOT/THistView.h
/// \ingroup Hist ROOT7
/// \author Axel Naumann <axel@cern.ch>
/// \date 2015-08-06
/// \warning This is part of the ROOT 7 prototype! It will change without notice. It might trigger earthquakes. Feedback
/// is welcome!

/*************************************************************************
 * Copyright (C) 1995-2015, Rene Brun and Fons Rademakers.               *
 * All rights reserved.                                                  *
 *                                                                       *
 * For the licensing terms see $ROOTSYS/LICENSE.                         *
 * For the list of contributors see $ROOTSYS/README/CREDITS.             *
 *************************************************************************/

#ifndef ROOT7_THistView
#define ROOT7_THistView

#include "ROOT/THist.hxx"

namespace ROOT {
namespace Experimental {

/*
 * Need THist::iterator for full range, takes a predicate for "in range?"
 * Returns true for THist; for THistView, checks range, returns false if not in
 * range. i+= 7 then does i++ seven times and checks at each step.
 * iterator is simply an int with a predicate functor. end is end of the
 * histogram - i.e. the number of bins (incl over / underflow).
 *
 * Add is then an operation (through a functor) on two bins.
 *
 * Drawing: need adaptor from THist<n,p>::GetBinContent(...) to
 * THistPrecNormalizer<n>::Get(i) that casts the bin content to a double. That
 * should be in internal but outside the drawing library (that needs to
 * communicate through abstract interfaces and can thus not instantiate
 * templates with user precision parameters.
 */

template <class HISTVIEW>
struct THistViewOutOfRange {
   HISTVIEW &fHistView;
   bool operator()(int idx) { return fHistView.IsBinOutOfRange(idx); }
};

/**
 \class THistView
 A view on a histogram, selecting a range on a subset of dimensions.
 */
template <int DIMENSIONS, class PRECISION, template <int D_, class P_, template <class P__> class S_> class... STAT>
class THistView {
public:
   using Hist_t = THist<DIMENSIONS, PRECISION, STAT...>;
   using AxisRange_t = typename Hist_t::AxisIterRange_t;
   using HistViewOutOfRange_t = THistViewOutOfRange<THistView>;

   using const_iterator = Detail::THistBinIter<typename Hist_t::ImplBase_t>;

   THistView(Hist_t &hist, int nbins, const AxisRange_t &range): fHist(hist), fNBins(nbins), fRange(range) {}

   bool IsBinOutOfRange(int idx) const noexcept
   {
      // TODO: use fRange!
      return idx < 0 || idx > fNBins;
   }

   void SetRange(int axis, double from, double to)
   {
      TAxisView axisView = fHist.GetImpl()->GetAxis(axis);
      fRange[axis] = axisView.FindBin(from);
      fRange[axis] = axisView.FindBin(to);
   }

   const_iterator begin() const noexcept
   {
      int beginidx = 0;
      size_t nbins = fHist.GetNBins();
      while (IsBinOutOfRange(beginidx) && beginidx < nbins)
         ++beginidx;
      return const_iterator(beginidx, HistViewOutOfRange_t(*this));
   }

   const_iterator end() const noexcept { return const_iterator(fHist.GetImpl(), fHist.GetImpl().GetNBins()); }

private:
   Hist_t &fHist;
   int fNBins = 0;
   AxisRange_t fRange;
};

} // namespace Experimental
} // namespace ROOT

#endif