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BUG: boolean indexing error with .drop()

See original GitHub issue

Code Sample, a copy-pastable example if possible

df = pd.DataFrame( data = {
                         'acol'  : np.arange(4),
                         'bcol' :  2*np.arange(4)
                        })
df.drop(df.bcol > 2, axis=0, inplace=True)

print(df)

Expected Output

	acol	bcol
0	0	0
1	1	2

Observed Output

	acol	bcol
2	2	4
3	3	6
4	4	8

Problem description

The anticipated behavior was that rows with bcol > 2 would be dropped. The actual behavior is that the boolean gets converted to 0/1, and then treated as index label. So row numbers 0 and/or 1 are dropped… but all other rows will be kept.

The documentation did not make it clear what was happening.

Solutions might include documentation clarifying that .drop() cannot be used with boolean indexing, or a warning when receiving the (attempted) boolean index.

Output of `pd.show_versions()`

INSTALLED VERSIONS ------------------ commit: None python: 3.6.1.final.0 python-bits: 64 OS: Linux OS-release: 2.6.32-573.12.1.el6.x86_64 machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: en_US.UTF-8

pandas: 0.20.2 pytest: 3.1.2 pip: 9.0.1 setuptools: 33.1.1.post20170320 Cython: 0.25.2 numpy: 1.12.1 scipy: 0.19.1 xarray: 0.9.6 IPython: 6.1.0 sphinx: 1.6.3 patsy: 0.4.1 dateutil: 2.6.0 pytz: 2017.2 blosc: None bottleneck: 1.2.0 tables: 3.4.2 numexpr: 2.6.2 feather: None matplotlib: 2.0.2 openpyxl: 2.5.0a1 xlrd: 1.0.0 xlwt: 1.2.0 xlsxwriter: 0.9.6 lxml: 3.8.0 bs4: 4.5.3 html5lib: 0.9999999 sqlalchemy: 1.1.11 pymysql: 0.7.9.None psycopg2: 2.7.1 (dt dec pq3 ext lo64) jinja2: 2.9.5 s3fs: 0.1.1 pandas_gbq: None pandas_datareader: None