Re: [Boost-users] chaining ouput iterator to input iterator

Subject: Re: [Boost-users] chaining ouput iterator to input iterator
From: MM (finjulhich_at_[hidden])
Date: 2012-07-08 17:33:58

> -----Original Message-----
> From: boost-users-bounces_at_[hidden] [mailto:boost-users-
> bounces_at_[hidden]] On Behalf Of Nathan Ridge
> Sent: 08 July 2012 15:33
> To: Boost Mailing List
> Subject: Re: [Boost-users] chaining ouput iterator to input iterator
> 
> 
> > > > I have a function that transforms a serie of numbers into another
> > > serie:
> > > >
> > > > template <typename InputIterator, typename OutputIterator>
> > > > void mytransform( InputIterator begin, InputIterator end,
> > > OutputIterator out )
> > > > {
> > > > }
> > > >
> > > >
> > > > and a 2nd function that calculates the standard deviation of a
> sample
> > > >
> > > > template <typename InputIterator >
> > > > double stdev( InputIterator begin, InputIterator end)
> > > > {
> > > > }
> > > >
> > > > Is there a way to chain these existing functions in order to get
> the
> > > std dev
> > > > of the transformed serie, without storing the intermediate
> numbers?
> > > > Maybe with the help of some lazy iterator, or some lazy function?
> > >
> > > In this particular case, you can use boost::transform_iterator
> rather
> > > than std::transform, as Jeff pointed out.
> > >
> > > However, this does not resolve the problem in general, which is how
> to
> > > treat the sequence of values a function writes to an output
> iterator as
> > > a range (or pair of iterators) input to another function (without
> > > accumulating the elements in a container, of course).
> >
> > I'm not too sure how to call the transform_iterator in this case.
> >
> > I have these 2 functions that I need to provide separately because
> they are
> > used separately.
> > And I also need a 3rd function, called
> >
> > double stddev_of_transformed(InputIterator begin, InputIterator end)
> > {
> > return mytransform(begin, end, boost::transform_iterator( ... ) ); //
> > ????
> > }
> 
> Sorry, I thought by transform() you meant std::transform(). If you have
> your
> own mytransform() function (and you can't replace it with a call to
> std::transform()), then boost::transform_iterator may not be
> applicable. In
> that case, your options are 1) accumulate the outputs in a container in
> between the two calls, or 2) use a Boost.Context-based solution as I
> mentioned before.
> 
> Regards,
> Nate

Boost.Coroutine? Is that in boost vault?

MM