CompareByIndex.hh
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CompareByIndex.hh
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	#ifndef NPSTAT_COMPAREBYINDEX_HH_
	#define NPSTAT_COMPAREBYINDEX_HH_

	/*!
	// \file CompareByIndex.hh
	//
	// \brief Compare subscriptable objects (e.g., vectors) by their k-th element
	//
	// Author: I. Volobouev
	//
	// March 2010
	*/

	namespace npstat {
	/**
	// Comparison functor for classes which support subscripting and for
	// pointers to such classes. To be used with std::sort and such.
	*/
	template <typename T>
	class LessByIndex
	{
	public:
	/** Constructor takes the index of the element to be compared */
	inline explicit LessByIndex(const unsigned i) : i_(i) {}

	inline bool operator()(const T& x, const T& y) const
	{return x[i_] < y[i_];}
	inline bool operator()(const T* x, const T* y) const
	{return (x)[i_] < (y)[i_];}
	private:
	LessByIndex();
	unsigned i_;
	};

	/**
	// Comparison functor for classes which support subscripting and for
	// pointers to such classes. To be used with std::sort and such.
	*/
	template <typename T>
	class GreaterByIndex
	{
	public:
	/** Constructor takes the index of the element to be compared */
	inline explicit GreaterByIndex(const unsigned i) : i_(i) {}

	inline bool operator()(const T& x, const T& y) const
	{return y[i_] < x[i_];}
	inline bool operator()(const T* x, const T* y) const
	{return (y)[i_] < (x)[i_];}
	private:
	GreaterByIndex();
	unsigned i_;
	};
	}

	#endif // NPSTAT_COMPAREBYINDEX_HH_