Re: [boost] [accumulators]Couple notes

From: Eric Niebler (eric_at_[hidden])
Date: 2007-02-16 15:19:57

Gennadiy Rozental wrote:
> Hi,
> 
>   I did not have a change to participate in a review because I was busy at 
> the time(as it is usual lately). I did like the submission when it 
> originally appeared. And now after reading docs some more I could only 
> congratulate Eric for yet another good addition to the boost.

Thanks!

>   Being the author of similar (though obviously not that powerful) component 
> myself I find two featured omitted. I must admit that I may've easily missed 
> something. But here we go.
> 
> 1. accumulator composition
> 
> It would be a pity if I need to write new accumulator any time I need to 
> combine features implemented by two existing one. For example
> 
> min/max average value
> min/max change rate

Sorry, I don't understand. A data series has one average. What is the 
max average?

> 2. timing policy.
> In many of my real life projects that require some statistical value it 
> almost always need to be combined with the time of the event. For example
> 
> when particular value reached it's maximum?
> when particular value reached it's minimum?
> when particular value was last changed?
> 
> or more specific:
> 
> When 10 sec throughput average reached it's maximum?
> 
> similar idea could be applied to any statistics that model some extreme 
> value. IMO framework should support this in a form of timing policy 
> somewhere.

You could implement this with accumulators either using covariate data, 
where the times are covariate with the samples, or by using a std::pair< 
sample, time > as the value type of the accumulator, and defining an 
appropriate sort criterion.

> Another general comment. I personally would find single changing variable 
> oriented interface more convenient and ore widely applicable (as opposed to 
> the samples set). Variable could change in many ways (not only addition or 
> subtraction, and even those  could be done more conveniently with operator 
> overloading). Essentially what I am looking for is something like this:
> 
> tracked_var<....> v;
> 
> v += 10;
> 
> int i = v +1;
> 
> v -= 5;
> 
> v *= 2;
> 
> cout << average( v );
> cout << max( v );
> cout << min( v );
> 
> cout << max( average( v ) ) << " @" min( average( v ) ).time();

Interesting. Each mutating operation on v is considered a new sample? 
This is a less powerful interface (no way to express covariate data; 
eg., where is the time of each sample specified?), but might be cleaner 
for some applications. It would be pretty simple to implement such an 
interface on top of accumulator_set.

-- 
Eric Niebler
Boost Consulting
www.boost-consulting.com