Natural breaks (Jenks) classes not computed correctly from expression

[qgib]

Author Name: Joshua Biagio (@roehnan)
Original Redmine Issue: 20479
Affected QGIS version: 3.4.1
Redmine category:symbology

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QGIS doesn't compute the classes using Natural Breaks (Jenks) correctly. The first class only has one value and the subsequent classes are wrong.

Here are the classes as they should be computed:

Here are the classes that QGIS computes:

Note that the first class is value - same value. Also affects v3.2.3.

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• ArcMapCorrectJenks.png (Joshua Biagio)
• QGISIncorrectJenks.png (Joshua Biagio)
• totalreg.shp.zip (Joshua Biagio)

[qgib]

Author Name: Giovanni Manghi (@gioman)

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Can you attach a sample of the data?

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• status_id was changed from Open to Feedback
• category_id was changed from Unknown to Symbology

[qgib]

Author Name: Joshua Biagio (@roehnan)

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Giovanni Manghi wrote:

Can you attach a sample of the data?

Here is a shapefile that contains the sample data. You'll need to set the column as an expression: "Reg_Total" / "POP2000".

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• 13768 was configured as totalreg.shp.zip

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• totalreg.shp.zip (Joshua Biagio) - shapefile with sample data

[qgib]

Author Name: Giovanni Manghi (@gioman)

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• operating_system was changed from Windows 10 64-bit to
• status_id was changed from Feedback to Open

[gioman]

Still true on the latest master.

[Pedro-Murteira]

Can still replicate this issue on QGIS 3.16.14 and 3.22.1.