Defer to iloc when indexer is an integer-like object and the Index is non-numeric dtype

[skirui-source]

Pandas interprets idx in the expression sr[idx] as an absolute position in the series sr when idx's dtype is different from that of sr's Index.

In Pandas, the indexing takes both an integer and a string as the index:

>>> import pandas as pd
>>> x = pd.Series([1,2,3], index=pd.Index(["a", "b", "c"]))
>>> x["b"]
2
>>> x[1]
2

Whereas cuDF treats idx as a value to look up in sr's Index, which can lead to different behaviors when indices have non-integral dtypes:

>>> import cudf
>>> x = cudf.Series([1,2,3], index=cudf.Index(["a", "b", "c"]))
>>> x["b"]
2
>>> x[1]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/nfs/wonchanl/anaconda3/envs/rapids-tpcx-bb/lib/python3.7/site-packages/cudf/core/series.py", line 921, in __getitem__
    return self.loc[arg]
  File "/home/nfs/wonchanl/anaconda3/envs/rapids-tpcx-bb/lib/python3.7/site-packages/cudf/core/indexing.py", line 120, in __getitem__
    raise KeyError(arg)
KeyError: 1

This PR fixes the mismatch behavior in cuDF by deferring to iloc when a Series has a non-numerical Index and the indexer idx is an integer-like value : int, cudf Scalar, numpy int [np.int8, np.uint32, int64,,,]

Fixes: #7622
Replaces: #7775

[codecov]

Codecov Report

Merging #7897 (afcf79a) into branch-0.20 (51336df) will increase coverage by 0.02%.
The diff coverage is 88.88%.

❗ Current head afcf79a differs from pull request most recent head c06335f. Consider uploading reports for the commit c06335f to get more accurate results

@@               Coverage Diff               @@
##           branch-0.20    #7897      +/-   ##
===============================================
+ Coverage        82.88%   82.91%   +0.02%     
===============================================
  Files              103      103              
  Lines            17668    17660       -8     
===============================================
- Hits             14645    14643       -2     
+ Misses            3023     3017       -6     

Impacted Files	Coverage Δ
python/cudf/cudf/core/column/__init__.py	100.00% <ø> (ø)
python/cudf/cudf/utils/cudautils.py	57.75% <25.00%> (ø)
python/cudf/cudf/core/column/column.py	88.64% <71.42%> (ø)
python/cudf/cudf/core/column/numerical.py	94.43% <72.72%> (ø)
python/cudf/cudf/core/dataframe.py	90.87% <83.33%> (+0.01%)	⬆️
python/cudf/cudf/utils/utils.py	89.53% <91.66%> (+0.02%)	⬆️
python/cudf/cudf/core/column/datetime.py	89.91% <100.00%> (ø)
python/cudf/cudf/core/column/timedelta.py	88.66% <100.00%> (ø)
python/cudf/cudf/core/groupby/groupby.py	92.28% <100.00%> (+0.83%)	⬆️
python/cudf/cudf/core/index.py	93.07% <100.00%> (ø)
... and 18 more

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[vyasr]

Side note: for titles and descriptions, let's be descriptive of what's introduced in the PR. When github squash merges, all that's left for the PR is the code, the title and the description. It's important we keep a trace of what's introduced. Example: 8dc1559

It also doesn't have to be an echo of the issue you are addressing to. Sometimes your PR addresses part of the issue, other times it adds more stuff outside of the scope of the issue.

@isVoid very good point, maybe post this in Slack to make it more visible to everyone? Especially with regard to the PR description, often people write initial descriptions with questions for the reviewers or requests for help, so it would be good to have the final description updated before PRs get merged.

[isVoid]

lgtm!

[kkraus14]

rerun tests

[kkraus14]

@gpucibot merge