BUG GH16983 fix df.where with extension dtypes

[JustinZhengBC]

• closes BUG: DataFrame.astype with category dtype #16983???
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

The referenced issue showcases two bugs. I was not able to replicate the first one, but I tracked down the cause of the ndim ValueError in the second example. An ExtensionBlock passed to df.where used to be unpacked here into a 1D array while normal blocks are unpacked earlier here into a 2D nx1 array.

[pep8speaks]

Hello @JustinZhengBC! Thanks for submitting the PR.

• There are no PEP8 issues in the file pandas/core/internals/blocks.py !

• There are no PEP8 issues in the file pandas/tests/frame/test_indexing.py !

[codecov]

Codecov Report

Merging #24169 into master will increase coverage by 49.18%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           master   #24169       +/-   ##
===========================================
+ Coverage   43.02%   92.21%   +49.18%     
===========================================
  Files         162      162               
  Lines       51700    51702        +2     
===========================================
+ Hits        22245    47675    +25430     
+ Misses      29455     4027    -25428

Flag	Coverage Δ
#multiple	90.61% <100%> (?)
#single	43.02% <0%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
pandas/core/internals/blocks.py	93.66% <100%> (+40.79%)	⬆️
pandas/core/computation/pytables.py	92.37% <0%> (+0.3%)	⬆️
pandas/io/pytables.py	92.3% <0%> (+0.92%)	⬆️
pandas/util/_test_decorators.py	93.24% <0%> (+4.05%)	⬆️
pandas/compat/__init__.py	58.3% <0%> (+8.1%)	⬆️
pandas/core/config_init.py	99.24% <0%> (+9.84%)	⬆️
pandas/core/reshape/util.py	100% <0%> (+11.53%)	⬆️
pandas/compat/numpy/__init__.py	92.85% <0%> (+14.28%)	⬆️
pandas/core/computation/common.py	85.71% <0%> (+14.28%)	⬆️
pandas/core/api.py	100% <0%> (+14.81%)	⬆️
... and 120 more

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[codecov]

Codecov Report

Merging #24169 into master will increase coverage by 49.18%.
The diff coverage is 100%.

@@             Coverage Diff             @@
##           master   #24169       +/-   ##
===========================================
+ Coverage   43.02%   92.21%   +49.18%     
===========================================
  Files         162      162               
  Lines       51700    51702        +2     
===========================================
+ Hits        22245    47675    +25430     
+ Misses      29455     4027    -25428

Flag	Coverage Δ
#multiple	90.61% <100%> (?)
#single	43.02% <0%> (-0.01%)	⬇️

Impacted Files	Coverage Δ
pandas/core/internals/blocks.py	93.66% <100%> (+40.79%)	⬆️
pandas/core/computation/pytables.py	92.37% <0%> (+0.3%)	⬆️
pandas/io/pytables.py	92.3% <0%> (+0.92%)	⬆️
pandas/util/_test_decorators.py	93.24% <0%> (+4.05%)	⬆️
pandas/compat/__init__.py	58.3% <0%> (+8.1%)	⬆️
pandas/core/config_init.py	99.24% <0%> (+9.84%)	⬆️
pandas/core/reshape/util.py	100% <0%> (+11.53%)	⬆️
pandas/compat/numpy/__init__.py	92.85% <0%> (+14.28%)	⬆️
pandas/core/computation/common.py	85.71% <0%> (+14.28%)	⬆️
pandas/core/api.py	100% <0%> (+14.81%)	⬆️
... and 120 more

---

Continue to review full report at Codecov.

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[TomAugspurger]

#24114 is fixing this.

[TomAugspurger]

Just FYI, we want to avoid get_values since that converts the ExtensionArray to an ndarray.