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

[Paolo Cavallini]

hI rICHARD,

On 02/03/19 08:41, Richard Duivenvoorde wrote:
> Hi,
> 
> I've been asked to see if I can add 'logarithmic' breaks to the
> GraduatedSymbolRenderer.
> I am right that it is missing, yes?
> 
> BUT: looking into current code and testing the available break modes I
> happen to look at the Quantile (Equal Count) one with a random dataset I
> had around:
> 
> https://duif.net/temp/QuantileEqualCount.png
> 
> Using more classes makes it even worse:
> 
> https://duif.net/temp/QuantileEqualCount2.png
> 
> As you see a lot of 'empty' zero classes.
> If I google: "The quantile map tries to bin the same count of features
> in each of the x classes."
> 
> As if the 'breaks'-algorithm cannot handle zero's or floats or negative
> values ???
> 
> The spread is indeed funny, see:
> 
> https://duif.net/temp/EqualInterval.png
> 
> What do others think?
> Am I misunderstanding things or is my data borked?

we also noticed that for large data sets (tens of thousands records)
`Pretty breaks` classification behaves strangely: when clicking on
Classify repeatedly, classes boundaries change by about 10% all the
time, apparently in a random fashion.
Unsure whether this is the same or a different issue.
All the best.
-- 
Paolo Cavallini - www.faunalia.eu
QGIS.ORG Chair:
http://planet.qgis.org/planet/user/28/tag/qgis%20board/