[Boost-users] [accumulators] accumulator "adapters"?

Subject: [Boost-users] [accumulators] accumulator "adapters"?
From: Pete Bartlett (pete_at_[hidden])
Date: 2013-01-25 11:05:52

Dear all,
 
The accumulators library is a very nice way to get a set of statistics for a stream of numbers, doubles, say.
Now let’s suppose I’m receiving a stream of boost::optional<double>s – e.g. let’s suppose I’m receiving simulation results and some simulations fail.
It would be neat if I could somehow write and “adaptor accumulator” that took this stream of optionals and then, if they are not empty, pass them to an underlying accumulator.
 
In rough terms:
 
template<typename UnderlyingAccumulator , typename Sample > struct accumulator_adaptor
{
            template<typename Args> void operator()( Args const& args)
            {
                        Sample const& s = args[sample];
                        if( s )
                        {
                                    m_underlying_accumulator( *s ) ; //doesn’t compile UnderlyingAccumulator expects an Args, not a Sample
                        }
            }
 
private:
            UnderlyingAccumulator m_underlying_accumulator;
};
 
(we might also define another accumulator that just counts the number of “bad” samples.
Then by adding an appropriate feature adaptor, one could write something like
 
accumulator_set< boost::optional<double> ,  tag::accumulator_adaptor< mean > , tag::bad_samples_count >
 
For the data 1.0,2.0,boost::optional<double>(),4.0
 
This would return a mean of 7/3 and a bad_samples_count of 1.
 
Is it possible for me to implement such an adaptor that would work for an arbitrary underlying accumulator?
 
Thanks for your interest,
Pete