PERF: improve get_loc on unsorted, non-unique indexes

[toobaz]

• closes Int64Index.get_loc() is very slow on unsorted, non-unique index #19478
• tests passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

asv run:

     [bd4332f4]       [9ac7be34]
-         475±5μs          422±7μs     0.89  multiindex_object.Duplicates.time_remove_unused_levels
-      15.4±0.3ms       13.5±0.2ms     0.88  multiindex_object.GetLoc.time_small_get_loc_warm
-         197±5ns          171±2ns     0.87  index_object.Datetime.time_is_dates_only
-      8.68±0.3μs       6.88±0.1μs     0.79  index_object.Float64IndexMethod.time_get_loc
-          15.4μs       12.0±0.2μs     0.78  index_object.Indexing.time_get_loc_sorted('Float')
-         283±9μs          215±2μs     0.76  multiindex_object.Values.time_datetime_level_values_sliced
-          15.0μs           11.1μs     0.74  index_object.Indexing.time_get_loc('Float')
-     7.38±0.04μs      5.03±0.05μs     0.68  index_object.Indexing.time_get_loc_sorted('Int')
-     7.15±0.04μs      4.58±0.04μs     0.64  index_object.Indexing.time_get_loc('Int')
-       121±0.9ms           1.62ms     0.01  index_object.Indexing.time_get_loc_non_unique_sorted('Float')
-           136ms           1.51ms     0.01  index_object.Indexing.time_get_loc_non_unique('Float')
-         166±1ms      1.29±0.03ms     0.01  index_object.Indexing.time_get_loc_non_unique_sorted('Int')
-       175±0.9ms      1.29±0.01ms     0.01  index_object.Indexing.time_get_loc_non_unique('Int')

SOME BENCHMARKS HAVE CHANGED SIGNIFICANTLY.

[codecov]

Codecov Report

Merging #19539 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #19539   +/-   ##
=======================================
  Coverage   91.81%   91.81%           
=======================================
  Files         153      153           
  Lines       49481    49481           
=======================================
  Hits        45430    45430           
  Misses       4051     4051

Flag	Coverage Δ
#multiple	90.21% <ø> (ø)	⬆️
#single	41.85% <ø> (ø)	⬆️

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[jreback]

seems to be failing 2.7 on windows and a gazillion warnings

 C:\projects\pandas\pandas\core\indexes\base.py:1726: DeprecationWarning: using a non-integer number instead of an integer will result in an error in the future
    return getitem(key)
  C:\projects\pandas\pandas\core\indexes\base.py:1726: DeprecationWarning: using a non-integer number instead of an integer will result in an error in the future
    return getitem(key)
  C:\projects\pandas\pandas\core\indexes\base.py:1726: DeprecationWarning: using a non-integer number instead of an integer will result in an error in the future
    return getitem(key)
  C:\projects\pandas\pandas\core\indexes\base.py:1726: DeprecationWarning: using a non-integer number instead of an integer will result in an error in the future
    return getitem(key)
  C:\projects\pandas\pandas\core\indexes\base.py:1726: DeprecationWarning: using a non-integer number instead of an integer will result in an error in the future
    return getitem(key)

[jreback]

also can you see if this closes other issues as well (a couple of refernces in OP)

[toobaz]

@jreback : fixed (wasn't that hard!), ping.

(I guess it shouldn't harm to include in 0.23.0)

[jreback]

@toobaz lgtm. can you just update the asv's as the top with latest code

[toobaz]

can you just update the asv's as the top with latest code

Done.

[jreback]

thanks @toobaz