Hi Phil,
That would be great! I think adding third, fourth moments and skewness,
kurtosis would be a very useful addition.
Also, considering the formulas in Pebay, perhaps a method like
void merge(SummaryStatistics ss) {
// use Pebay update formulas to merge un-normalized moments of ss with
"this"
// if one is singleton use "update" method instead
}
could be added to SummaryStatistics in addition to "update". I realize
AggregateSummaryStatistics takes care of merging 1st,2nd order stats, so
this may be redundant.
If there is something I can do to help, please let me know.
-Mike Brzustowicz
On Wed, Dec 23, 2015 at 5:44 AM, Phil Steitz <[email protected]> wrote:
> On 12/22/15 9:58 AM, [email protected] wrote:
> > Hi,
> >
> > I see that
> org.apache.commons.math3.stat.descriptive.DescriptiveStatistics
> > uses the singleton update formulas (from Pebay) for calculating
> > (un-normalized) moments up to the 4th moment. Is there some reason that
> > org.apache.commons.math3.stat.descriptive.SummaryStatistics excludes both
> > third and fourth central moments?
> >
> > Is it just a matter of computational efficiency, ie.
> DescriptiveStatistics
> > calculates moments only when the getter is invoked (and all orders need
> not
> > be calculated at once) while the "storeless" SummaryStatistics would need
> > to calculate all 4 orders at every call to update()?
>
> Yes, that is the reason; but it is really more a matter of no one
> having asked for this feature. You are correct that the updating
> formulas make this possible and the nested nature of the moments
> means that there should not be much cost to adding the third and
> fourth moments. I would be happy to review and apply a patch (with
> tests) adding these.
>
> Phil
>
> > Or is there some other
> > blocker?
> >
> > Thanx,
> > Mike Brzustowicz
> >
>
>
>
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