Re: [Boost-users] [Accumulators] Are all statistics lazily evaluated by default?

Subject: Re: [Boost-users] [Accumulators] Are all statistics lazily evaluated by default?
From: Eric Niebler (eric_at_[hidden])
Date: 2009-05-11 20:59:05

pete_at_[hidden] wrote:
> Hi all,
> 
> I really like the range of statistical properties that the accumulators 
> library supports but am a little unclear about the laziness properties 
> of the library.
> 
> Suppose I wish to offer a interface that lets the user send a bunch of 
> data and request the k-th moments where k is specified by the user at 
> runtime. Will the accumulator_set
> 
> accumulator_set< value_type , ba::tag::moments<k_max> > acc;
> 
> where k_max >= k (but the inequality may be strict) be efficient. I.e. I 
> only do the calculations necessary to get the k-th moment not the 
> k-max-th? The reason I ask is the documentation makes a distinction 
> between variance and lazy_variance, but this distinction does not seem 
> to be made for other statistics.

Hi,

The accumulators library doesn't mandate laziness or eagerness. As 
you've noticed, some accumulators come in lazy or eager flavors. Each 
accumulator defines an operator() that accepts a sample and a result() 
function that extracts the result. Whether the bulk of the work gets 
done in operator() (eager) or in result() (lazy) is up to you.

HTH,

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com