hv.Bars with more than one kdim randomly generates incorrect x-ticks in some cases (matplotlib backend)

[sztal]

As in the title

ALL software version info

(this library, plus any other relevant software, e.g. bokeh, python, notebook, OS, browser, etc)

• python=3.11
• holoviews=1.18.3
• pandas=2.2.2

Description of expected behavior and the observed behavior

hv.Bars should display x-tick values correctly in all cases instead of making some random errors from time to time in a way which is completely unpredictable.

Complete, minimal, self-contained example code that reproduces the issue

import json
import pandas as pd
import holoviews as hv

hv.extension("matplotlib", logo=False)

json1 = '{"Pet":{"0":"Cat","1":"Cat","2":"Dog","3":"Dog","4":"Hamster","5":"Hamster","6":"Rabbit","7":"Rabbit"},"Gender":{"0":"Female","1":"Male","2":"Female","3":"Male","4":"Female","5":"Male","6":"Female","7":"Male"},"Count":{"0":26,"1":21,"2":36,"3":24,"4":27,"5":34,"6":39,"7":39}}'

json2 = '{"community":{"0":"Concerned","1":"Concerned","2":"Concerned","3":"Informants","4":"Informants"},"stance":{"0":"Dystopia","1":"Pragmatic","2":"Protect","3":"Dystopia","4":"Pragmatic"},"len":{"0":25,"1":41,"2":30,"3":1,"4":56}}'

df1 = pd.DataFrame(json.loads(json1))
df2 = pd.DataFrame(json.loads(json2))

For df1 it works.

hv.Bars(df1, kdims=["Pet", "Gender"])

But for df2 it does not work correctly for some mysterious reasons. Note that the lower values for x-ticks are incorrect (both groups are labelled as "Pragmatic" which is a value of stance variable not community) and display one of the levels of stance variable instead of displaying values of community column (`"Concerned" and "Informants").

hv.Bars(df2, kdims=["community", "stance"])

Please explain to me what is going on here, because it is extremely confusing. I really want to love holoviews because it has a lot of killer features, but sometimes it behaves in so cryptic unpredicable ways that makes it really painful to work with it.

Stack traceback and/or browser JavaScript console output

Screenshots or screencasts of the bug in action

• I may be interested in making a pull request to address this

[hoxbro]

If I understand you correctly, this is fixed in #6145 (not yet merged):

Current behavior:

[sztal]

Great, thanks, I hope this will solve the issue. However, I still do not understand what makes any of the axes continuous? The two grouping variables are clearly discrete.

[hoxbro]

The bug was discovered and fixed in the PR. So, it is not directly related to the title.

See https://github.com/holoviz/holoviews/pull/6145/files#r1589356958