New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Subclassing is lost when using DataFrame.apply #19822

Closed
jaumebonet opened this Issue Feb 21, 2018 · 0 comments

Comments

Projects
None yet
2 participants
@jaumebonet
Contributor

jaumebonet commented Feb 21, 2018

Code Sample, a copy-pastable example if possible

import pandas as pd

# Define a subclass of Series
class ExtendedSeries( pd.Series ):
    @property
    def _constructor(self):
        return ExtendedSeries

# Define a subclass of DataFrame that slices into the ExtendedSeries class
class ExtendedFrame( pd.DataFrame ):
    @property
    def _constructor(self):
        return ExtendedFrame
    _constructor_sliced = ExtendedSeries

# Declare instance of ExtendedFrame
df = ExtendedFrame({"c1": [1, 2, 3, 4], "c2": [2, 3, 4, 5], "c3": [3, 4, 5, 6]})

print(type(df))
# <class '__main__.ExtendedFrame'>

print(type(df.iloc[0]))
# <class '__main__.ExtendedSeries'>

for x in df.apply(lambda x: type(x), axis=1):
    print(x)
#<class 'pandas.core.series.Series'>
#<class 'pandas.core.series.Series'>
#<class 'pandas.core.series.Series'>
#<class 'pandas.core.series.Series'>

Problem description

The class type of the applied objects should still be <class '__main__.ExtendedSeries'> instead of going back to <class 'pandas.core.series.Series'>.

The issue here is that in pandas.core.apply, whenever the returning objects are generated, they are declared as DataFrame and Series instead of self.obj._constructor and self.obj._constructor_slice.

This behaviour makes it difficult to properly work with subclasses from pandas.

Expected Output

Following the initial code example, the expected output should be:

import pandas as pd

# Define a subclass of Series
class ExtendedSeries( pd.Series ):
    @property
    def _constructor(self):
        return ExtendedSeries

# Define a subclass of DataFrame that slices into the ExtendedSeries class
class ExtendedFrame( pd.DataFrame ):
    @property
    def _constructor(self):
        return ExtendedFrame
    _constructor_sliced = ExtendedSeries

# Declare instance of ExtendedFrame
df = ExtendedFrame({"c1": [1, 2, 3, 4], "c2": [2, 3, 4, 5], "c3": [3, 4, 5, 6]})

print(type(df))
# <class '__main__.ExtendedFrame'>

print(type(df.iloc[0]))
# <class '__main__.ExtendedSeries'>

for x in df.apply(lambda x: type(x), axis=1):
    print(x)
#<class '__main__.ExtendedSeries'>
#<class '__main__.ExtendedSeries'>
#<class '__main__.ExtendedSeries'>
#<class '__main__.ExtendedSeries'>

(note the change in the last printed lines)

Output of pd.show_versions()

INSTALLED VERSIONS

commit: None
python: 2.7.12.final.0
python-bits: 64
OS: Darwin
OS-release: 17.4.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None

pandas: 0.21.1
pytest: None
pip: 9.0.1
setuptools: 38.4.0
Cython: None
numpy: 1.14.0
scipy: 0.18.1
pyarrow: None
xarray: None
IPython: 5.4.1
sphinx: 1.6.6
patsy: 0.4.1
dateutil: 2.6.1
pytz: 2017.3
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: 2.1.1
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: 4.5.1
html5lib: 0.999999999
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None

@jaumebonet jaumebonet referenced this issue Feb 21, 2018

Merged

Keep subclassing in apply #19823

4 of 4 tasks complete

@jreback jreback added this to the 0.23.0 milestone Feb 22, 2018

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment