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I have checked that this issue has not already been reported.
I have confirmed this bug exists on the latest version of pandas.
I have confirmed this bug exists on the main branch of pandas.
Reproducible Example
importpandasaspdimporttempfile# str_list is a column of lists of stringsdf=pd.DataFrame(
{
"id": [1,2,3,4,5],
"str_list": [
["a", "aa", "aaa"],
["b", "bb","bbb", "bbbb"],
["c", "cc"],
["d"],
["e","ee","eee"]
]
})
# will output listtype(df['str_list'][0])
# Write to a feather file and read back the feather filedf.to_feather(tempfile.gettempdir()+"/df.feather")
df2=pd.read_feather(tempfile.gettempdir()+"/df.feather")
# will output numpy.ndarraytype(df2['str_list'][0])
Issue Description
When a dataframe with column of lists is written to feather or parquet formats and then subsequently read back the column of lists becomes column of numpy.ndarray.
A column of lists is especially useful for NLP tasks where the corpus needs to be a list of list of strings. Passing a column of ndarray breaks this and requires an intermediate step of converting each ndarray in the column to a list.
Expected Behavior
Expected behavior - If a column of lists is written to feather/parquet files, it should be read back as a column of lists and not numpy.ndarray.
FWIW - to_pickle and subsequent read_pickle don't have this issue as can be seen by the code below
Pandas version checks
I have checked that this issue has not already been reported.
I have confirmed this bug exists on the latest version of pandas.
I have confirmed this bug exists on the main branch of pandas.
Reproducible Example
Issue Description
When a dataframe with column of lists is written to feather or parquet formats and then subsequently read back the column of lists becomes column of numpy.ndarray.
A column of lists is especially useful for NLP tasks where the corpus needs to be a list of list of strings. Passing a column of ndarray breaks this and requires an intermediate step of converting each ndarray in the column to a list.
Expected Behavior
Expected behavior - If a column of lists is written to feather/parquet files, it should be read back as a column of lists and not numpy.ndarray.
FWIW -
to_pickle
and subsequentread_pickle
don't have this issue as can be seen by the code belowInstalled Versions
list
numpy.ndarray
INSTALLED VERSIONS
commit : 91111fd
python : 3.9.13.final.0
python-bits : 64
OS : Linux
OS-release : 5.19.16-200.fc36.x86_64
Version : #1 SMP PREEMPT_DYNAMIC Sun Oct 16 22:50:04 UTC 2022
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8
pandas : 1.5.1
numpy : 1.23.4
pytz : 2022.6
dateutil : 2.8.2
setuptools : 65.5.1
pip : 22.3.1
Cython : 0.29.32
pytest : None
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : 4.9.1
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.1.2
IPython : 8.6.0
pandas_datareader: None
bs4 : 4.11.1
bottleneck : 1.3.5
brotli : None
fastparquet : None
fsspec : 2022.10.0
gcsfs : None
matplotlib : 3.6.2
numba : 0.56.4
numexpr : 2.8.4
odfpy : None
openpyxl : 3.0.10
pandas_gbq : None
pyarrow : 10.0.0
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : 1.9.3
snappy : None
sqlalchemy : None
tables : None
tabulate : 0.9.0
xarray : 2022.11.0
xlrd : None
xlwt : None
zstandard : None
tzdata : None
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