sorting_utility.hpp
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sorting_utility.hpp
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			#ifndef SORTING_HPP
			#define SORTING_HPP

			#include <vector>
			#include <algorithm>

			/*! \brief Given a vector of data, it returns a vector of index
			* corresponding to the indices of each element after data sorting
			* in ascending (by default) order.
			* \param data a vector of interest.
			* \param ascending specifies that the index should be returned in
			* ascending order
			* \return the index after sorting.
			*/
			template<class T>
			std::vector<std::size_t> order(const std::vector<T>& data, bool ascending=true)
			{
			std::vector<std::size_t> index(data.size(), 0) ;

			for(std::size_t i=0; i<index.size(); i++)
			{ index[i] = i ; }

			sort(index.begin(), index.end(),
			[&](const int& a, const int& b)
			{ return (data[a] < data[b]) ; }
			) ;

			if(not ascending)
			{ std::reverse(index.begin(), index.end()) ; }

			return index ;
			}



			#endif // SORTING_HPP