ENH: do not sort resulting columns when sort=False

[ShawnZhong]

• closes pivot_table not displaying values columns in expected order #17041
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

Currently, pivot_table sorts the resulting columns even when sort=False. For example, the following code snippet produces the column ["age", "height"] in alphabetical order instead of the order in the original df or passed by values=.

import pandas as pd

df = pd.DataFrame(
    {
        "firstname": ["John", "Michael"],
        "lastname": ["Foo", "Bar"],
        "height": [173, 182],
        "age": [47, 33],
    }
)
result = df.pivot_table(index=["lastname", "firstname"], values=["height", "age"], sort=False)
print(result)

                    age  height
lastname firstname             
Foo      John        47     173
Bar      Michael     33     182

This PR fixes this issue by not sorting the resulting columns when sort=False

FYI, #17041 has some discussion about the order of the columns. PR #40954 added the keyword sort to pivot_table and was merged in v1.3.

[pep8speaks]

Hello @ShawnZhong! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2022-05-15 18:21:51 UTC

[jreback]

I think ok to close #17041 with this PR (if you can add a test for this).

also pls add a whatsnew note. put in reshaping bug fixes section for 1.5

[ShawnZhong]

I have added the whatsnew note and changed the PR description to close the issue.

Is there a specific case that you want me to add a test for?

[jreback]

thanks @ShawnZhong