On Fri, 22 Jan 2010 14:13:31 -0800 Jeffrey Hellrung <jhellrung@ucla.edu> wrote: On 1/23/10 12:35 AM, boost-request@lists.boost.org wrote:
For a recent project, I needed to inquire about a sequence of objects and make a determination as to whether the sequences were:
* Increasing * Strictly Increasing * Decreasing * Strictly Decreasing
Looking through STL, Boost documentation, Boost sources and headers and the Boost mailing lists I was able to find neither an existing algorithm or stateful unary predicate functor for accomplishing this for a pair of input iterators. However, I was a bit surprised considering that this seems like a sequence property query that would tend to come up fairly often and serve a general utility. Did I just fail to form the proper search/query or am I overestimating the general utility?
Is a smarter realization of this as an algorithm a potential candidate for boost::algorithm?
Perhaps std::adjacent_find and std::less is all you need, e.g., to determine if a sequence is decreasing?
I.e., a sequence is decreasing iff all adjacent pairs of elements xi, x[i+1] satisfies xi >= x[i+1] iff no adjacent pair of elements xi, x[i+1] satisfies xi < x[i+1] (assuming that (!>=) == (<)).
On Fri, 22 Jan 2010 15:24:32 -0800 Marshall Clow <mclow.lists@gmail.com> wrote:
I've got this floating around from a while back...
[ examples omitted ]
Marshall and Jeff: Thanks for the feedback. Marshall's feedback seems to indicate that, yes, there is likely general utility need for such functions and Jeff, you are correct that these algorithms are trivially composed from std::adjacent_find, std::not2 and std::{greater,less,greater_equal,less_equal}: namespace boost { namespace detail { template <typename ForwardIterator, typename BinaryPredicate> bool is_creasing(ForwardIterator first, ForwardIterator last, BinaryPredicate binary_pred) { return std::adjacent_find(first, last, std::not2(binary_pred)) == last; } } // namespace detail template <typename ForwardIterator> bool is_increasing(ForwardIterator first, ForwardIterator last) { typedef typename std::iterator_traits<ForwardIterator>:: value_type value_type; return detail::is_creasing(first, last, std::less_equal<value_type>()); } [ ... other three instances follow trivially ... ] } // namespace boost Unless there's any other feedback, I'll work on posting an implementation to Boost Vault. Regards, Grant