Skip to content
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

DataFrame.to_parquet raises fails when dataframe is empty #27339

Closed
CJStadler opened this issue Jul 11, 2019 · 1 comment

Comments

@CJStadler
Copy link
Contributor

commented Jul 11, 2019

Code Sample, a copy-pastable example if possible

import pandas as pd

df = pd.DataFrame()
pd.to_parquet('empty.parquet')

Problem description

DataFrame.to_parquet raises ValueError: parquet must have string column names when the dataframe has no columns. pyarrow and fastparquet both support writing empty dataframes so I don't think this restriction is necessary (see below script).

import fastparquet as fp
import pyarrow as pa
import pyarrow.parquet as pq
import pandas as pd

df = pd.DataFrame()
fn = 'empty.parquet'

# Test fastparquet
fp.write(fn, df)

# Test pyarrow
table = pa.Table.from_pandas(df)
pq.write_table(table, fn)

# This will fail
df.to_parquet(fn)

I'm happy to open a PR if it's agreed that this is an issue.

Output of pd.show_versions()

INSTALLED VERSIONS

commit: None
python: 3.7.3.final.0
python-bits: 64
OS: Darwin
OS-release: 18.6.0
machine: x86_64
processor: i386
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.24.2
pytest: None
pip: 19.1.1
setuptools: 41.0.1
Cython: None
numpy: 1.16.4
scipy: None
pyarrow: 0.14.0
xarray: None
IPython: None
sphinx: None
patsy: None
dateutil: 2.8.0
pytz: 2019.1
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: None
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml.etree: None
bs4: None
html5lib: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: None
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None
gcsfs: None

@WillAyd

This comment has been minimized.

Copy link
Member

commented Jul 11, 2019

Makes sense to me if you'd like to try a PR

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Projects
None yet
3 participants
You can’t perform that action at this time.