[QGIS-Developer] Quantile (Equal Count) broken or is data borked?

[Nyall Dawson]

On Mon, 4 Mar 2019 at 02:21, Richard Duivenvoorde <rdmailings at duif.net> wrote:
>
> On 03/03/2019 11.31, Richard Duivenvoorde wrote:
> >>> https://duif.net/temp/QuantileEqualCount2.png
> >> I can't reproduce. Maybe data set dependant?
> > I've created random data in a geopackage and created an issue for it
> >
> > https://issues.qgis.org/issues/21451
>
> Mmm, diving into this a little more (googling about Quantiles...), it
> appears this has to do with ordering/ranking the data and then set 'breaks'.
>
> So in this dataset there seems to be A LOT of values '0' so if you first
> order that dataset, then create the breaks/buckets, it is possible to
> have several 'buckets' in the 0 range? So this then is not so much an
> error in creating the breaks, but more the visualisation of the numbers
> in the classes (IF it is indeed ok, to have several 'classes' all having
> 0 both as min and as max value....).
> Then QGIS should divide the 0-values over the 3 buckets all containing
> zero's?

I had a look - as you suspect, it's impossible to divide your data
into 10 equal sized buckets based solely on the distribution of values
contained within it.

>
> OR am I just misusing a method?And should you not use this method in a
> dataset in which the distribution is so uneven?

That's my thoughts. You'll need to choose a different partitioning method.

Nyall

>
> Anybody more into this statistical theory then I am??
>
>
> Regards,
>
> Richard Duivenvoorde
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