BUG: fix indexing.py to make a copy of the indices (#20852)

[subhrm]

• closes np array indexer modified in iloc #20852
• tests added / passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

WIP. Reviewing the test cases and would add a test case to validate this fix.

[pep8speaks]

Hello @subhrm! Thanks for updating the PR.

Cheers ! There are no PEP8 issues in this Pull Request. 🍻

Comment last updated on May 07, 2018 at 16:55 Hours UTC

[codecov]

Codecov Report

Merging #20855 into master will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #20855      +/-   ##
==========================================
+ Coverage   91.77%   91.81%   +0.03%     
==========================================
  Files         153      153              
  Lines       49313    49479     +166     
==========================================
+ Hits        45259    45430     +171     
+ Misses       4054     4049       -5

Flag	Coverage Δ
#multiple	90.21% <ø> (+0.04%)	⬆️
#single	41.85% <ø> (-0.04%)	⬇️

Impacted Files	Coverage Δ
pandas/core/indexing.py	93.56% <ø> (+0.42%)	⬆️
pandas/core/frame.py	97.13% <0%> (-0.1%)	⬇️
pandas/core/indexes/timedeltas.py	91.15% <0%> (-0.07%)	⬇️
pandas/core/indexes/datetimes.py	95.73% <0%> (-0.04%)	⬇️
pandas/core/generic.py	95.94% <0%> (ø)	⬆️
pandas/core/reshape/pivot.py	96.97% <0%> (ø)	⬆️
pandas/core/panel.py	97.29% <0%> (ø)	⬆️
pandas/io/formats/latex.py	100% <0%> (ø)	⬆️
pandas/core/resample.py	96.07% <0%> (ø)	⬆️
pandas/core/reshape/concat.py	97.59% <0%> (ø)	⬆️
... and 13 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 563a6ad...6b0a872. Read the comment docs.

[jreback]

can you add

• whatsnew note
• tests (in tests/indexing/test_indexing.py)

[jreback]

can you move the copy to inside mask.any() check as its only needed there. use indices.copy()

[subhrm]

Thanks for your review comments. I have made the changes as suggested.

[subhrm]

Would add new testcases for this change .

[jorisvandenbossche]

@subhrm Can you update for @jreback 's questions:

• whatsnew note (a small note in v0.23.1.txt in the bug fixes section
• add a test (in tests/indexing/test_indexing.py). You can use the example in the issue, and then assert that the indexer array has not changed

[subhrm]

@jorisvandenbossche sorry I could not devote any time for this.
I would do the suggested changes and update by this weekend (10th June).
Thanks for reminding me.

[subhrm]

Implemented via PR #21867 . Closing this one.