ENH: Add DatetimeIndexResampler.nlargest · Issue #17791 · pandas-dev/pandas (original) (raw)

Code Sample, a copy-pastable example if possible

With this setup:

import numpy as np n = 1000 dates = pd.date_range(start='2010-01-01', periods=n) rain_random = pd.Series(data=np.random.uniform(size=n), index=dates)

these two operations given different results:

rain_random.groupby(rain_random.index.year).nlargest(3)

rain_random.resample('A').nlargest(3)

Problem description

The Series.resample().nlargest() operation is inconsistent with DataFrame.resample()[column].nlargest() and the groupby equivalent. It emits a warning

Output:

/Users/schofield/miniconda/envs/py36/lib/python3.6/site-packages/ipykernel_launcher.py:1: FutureWarning: 
.resample() is now a deferred operation
You called nlargest(...) on this deferred object which materialized it into a series
by implicitly taking the mean.  Use .resample(...).mean() instead
  """Entry point for launching an IPython kernel.
Out[427]:
2010-12-31    0.507550
2012-12-31    0.490082
2011-12-31    0.478356
dtype: float64

Expected output:

Date        Date      
1930-12-31  1930-10-06      288.135370
            1930-10-05      285.587734
            1930-10-07      259.439935
            1930-10-08      227.587389
            1930-10-09      190.054844
1931-12-31  1931-01-26     3052.104566
            1931-01-25     2839.126102
            1931-01-29     2196.167129
            1931-02-01     1953.331709
            1931-01-27     1893.975328
1932-12-31  1932-01-19     9526.953864
            1932-01-20     4278.291105
            1932-03-03     2952.348903
            1932-03-02     2946.385433
            1932-03-04     2098.108897

pd.show_versions() output:

INSTALLED VERSIONS

commit: None
python: 3.6.1.final.0
python-bits: 64
OS: Darwin
OS-release: 16.6.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: en_AU.UTF-8
LOCALE: en_AU.UTF-8

pandas: 0.20.1
pytest: 3.0.7
pip: 9.0.1
setuptools: 27.2.0
Cython: 0.25.2
numpy: 1.12.1
scipy: 0.19.0
xarray: None
IPython: 5.3.0
sphinx: 1.6.3
patsy: 0.4.1
dateutil: 2.6.0
pytz: 2017.2
blosc: None
bottleneck: 1.2.1
tables: 3.4.2
numexpr: 2.6.2
feather: None
matplotlib: 2.0.2
openpyxl: 2.4.7
xlrd: 1.0.0
xlwt: 1.2.0
xlsxwriter: 0.9.6
lxml: 3.7.3
bs4: 4.6.0
html5lib: 0.999
sqlalchemy: 1.1.9
pymysql: None
psycopg2: None
jinja2: 2.9.6
s3fs: None
pandas_gbq: None
pandas_datareader: 0.5.0