BUG: alignment bug when setting a subset of rows and attempting to switch columns · Issue #8258 · pandas-dev/pandas (original) (raw)

Originally posted at stackexchange:
http://stackoverflow.com/questions/25811529/setting-values-on-a-subset-of-rows-indexing-boolean-setting/25812825#25812825
Jeff suggested posting here also.

df = DataFrame({'L': ['left', 'right', 'left', 'right'], 'R': ['right', 'left', 'right', 'left'], 'idx': [False, True, False, True], 'num': np.arange(4) })

df1 = df.copy() df2 = df.copy() df3 = df.copy() df4 = df.copy()

#1 nothing happens (expected result) df1.loc[df1.idx,['L','R']] = df1.loc[df1.idx,['R','L']]

#2 something weird happens df2.loc[df2.idx,['L','R']] = df2[['R','L']]

Results below:

In [572]: df Out[572]: L R idx num 0 left right False 0 1 right left True 1 2 left right False 2 3 right left True 3

In [573]: df1 Out[573]: L R idx num 0 left right False 0 1 right left True 1 2 left right False 2 3 right left True 3

In [574]: df2 Out[574]: L R idx num 0 left right False 0 1 left right True 1 2 left right False 2 3 right left True 3

INSTALLED VERSIONS
------------------
commit: None
python: 2.7.7.final.0
python-bits: 64
OS: Windows
OS-release: 7
machine: AMD64
processor: Intel64 Family 6 Model 26 Stepping 5, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None

pandas: 0.14.1.dev
nose: 1.3.3
Cython: 0.20.1
numpy: 1.8.1
scipy: 0.14.0
statsmodels: 0.5.0
IPython: 2.1.0
sphinx: 1.2.2
patsy: 0.2.1
scikits.timeseries: None
dateutil: 1.5
pytz: 2014.3
bottleneck: None
tables: 3.1.1
numexpr: 2.3.1
matplotlib: 1.3.1
openpyxl: 1.8.5
xlrd: 0.9.3
xlwt: 0.7.5
xlsxwriter: 0.5.5
lxml: 3.3.5
bs4: 4.3.1
html5lib: None
httplib2: None
apiclient: None
rpy2: None
sqlalchemy: 0.9.4
pymysql: None
psycopg2: None