Added new algorithm 'sort_subrange' from Sean Parent's CppCon keynote. Docs to come

include/boost/algorithm/sort_subrange.hpp

@@ -0,0 +1,72 @@
+/* 
+   Copyright (c) Marshall Clow 2008-2012.
+
+   Distributed under the Boost Software License, Version 1.0. (See accompanying
+   file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+
+ Revision history:
+   28 Sep 2015 mtc First version
+   
+*/
+
+/// \file sort_subrange.hpp
+/// \brief Sort a subrange
+/// \author Marshall Clow
+///
+/// Suggested by Sean Parent in his CppCon 2015 keynote
+
+#ifndef BOOST_ALGORITHM_SORT_SUBRANGE_HPP
+#define BOOST_ALGORITHM_SORT_SUBRANGE_HPP
+
+#include <functional>       // For std::less
+#include <iterator>         // For std::iterator_traits
+#include <algorithm>        // For nth_element and partial_sort
+
+#include <boost/range/begin.hpp>
+#include <boost/range/end.hpp>
+
+namespace boost { namespace algorithm {
+
+/// \fn sort_subrange ( T const& val, 
+///               Iterator first,     Iterator last, 
+///               Iterator sub_first, Iterator sub_last, 
+///               Pred p )
+/// \brief Sort the subrange [sub_first, sub_last) that is inside
+///     the range [first, last) as if you had sorted the entire range.
+/// 
+/// \param first       The start of the larger range
+/// \param last        The end of the larger range
+/// \param sub_first   The start of the sub range
+/// \param sub_last    The end of the sub range
+/// \param p           A predicate to use to compare the values.
+///                        p ( a, b ) returns a boolean.
+///
+  template<typename Iterator, typename Pred> 
+  void sort_subrange (
+  	Iterator first,     Iterator last, 
+  	Iterator sub_first, Iterator sub_last,
+  	Pred p)
+  {
+  	if (sub_first == sub_last) return; // the empty sub-range is already sorted.
+  	
+  	if (sub_first != first) { // sub-range is at the start, don't need to partition
+  		(void) std::nth_element(first, sub_first, last, p);
+  		++sub_first;
+  		}
+  	std::partial_sort(sub_first, sub_last, last, p);
+  }
+
+
+
+  template<typename Iterator> 
+  void sort_subrange (Iterator first, Iterator last, Iterator sub_first, Iterator sub_last)
+  {
+  	typedef typename std::iterator_traits<Iterator>::value_type value_type;
+  	return sort_subrange(first, last, sub_first, sub_last, std::less<value_type>());
+  }
+
+/// range versions?
+
+}}
+
+#endif // BOOST_ALGORITHM_SORT_SUBRANGE_HPP