BUG: `to_parquet` failing for integer-like string values in categorical column

[RabeezRiaz]

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

# Happy to provide a reproducible example if someone can guide on *what* the example should be since the issue only seems to happen on my full series of raw data

Issue Description

I receive the following exception when trying df.to_parquet():

ArrowInvalid: ("Could not convert <pyarrow.StringScalar: '50015202101011004687846'> with type pyarrow.lib.StringScalar: did not recognize Python value type when inferring an Arrow data type", 'Conversion failed for column Ticket ID with type category')

This is the problematic column:

Same exception persists if I manually try to convert that whole column using pa.array():

ArrowInvalid: Could not convert <pyarrow.StringScalar: '50015202101011004687846'> with type pyarrow.lib.StringScalar: did not recognize Python value type when inferring an Arrow data type

Trying the same with a length 1 series for the value in the exception results in exactly the same exception

pa.array(df_full.loc[[15247763],"Ticket ID"])

but the conversion passes successfully if I remove unused categories through pandas beforehand:

pa.array(df_full.loc[[15247763],"Ticket ID"].cat.remove_unused_categories())

Expected Behavior

I can't understand what type arrow is trying to infer here, or why this expected type changes when I remove the categories for which their is no error.

Installed Versions

INSTALLED VERSIONS

commit : 4bfe3d0
python : 3.9.7.final.0
python-bits : 64
OS : Linux
OS-release : 5.13.0-1021-aws
Version : #23~20.04.2-Ubuntu SMP Thu Mar 31 11:36:15 UTC 2022
machine : x86_64
processor : x86_64
byteorder : little
LC_ALL : en_US.UTF-8
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 1.4.2
numpy : 1.19.5
pytz : 2021.3
dateutil : 2.8.2
pip : 21.3.1
setuptools : 58.0.4
Cython : None
pytest : 7.1.2
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 3.0.3
IPython : 7.32.0
pandas_datareader: None
bs4 : None
bottleneck : None
brotli :
fastparquet : 0.8.1
fsspec : 2021.10.1
gcsfs : None
markupsafe : 2.0.1
matplotlib : 3.3.4
numba : None
numexpr : 2.8.1
odfpy : None
openpyxl : 3.0.9
pandas_gbq : None
pyarrow : 7.0.0
pyreadstat : None
pyxlsb : None
s3fs : None
scipy : 1.8.0
snappy : None
sqlalchemy : 1.4.29
tables : 3.7.0
tabulate : None
xarray : None
xlrd : None
xlwt : None
zstandard : None

[RabeezRiaz]

Again, I'm more than happy to provide a reproducible example. I actually noticed the strange behaviour with remove_unused_categories() while trying to make an example but the issue didn't replicate.

If someone more familiar with arrow/pyarrow can suggest a useful example I can test and provide it here.

[rhshadrach]

Thanks for the report - can you try reducing your data down to a simple example that still demonstrates the issue? For example, you could try on just the 1st half and then the 2nd half and see which of these fails - hopefully one will. Then continue in this manner until it is reasonable to post.

[RabeezRiaz]

@rhshadrach I've tried your suggestion but the error doesn't consistently keep appearing if I keep slicing the series:

full_s = df_full["Ticket ID"].cat.remove_unused_categories()
pyarrow.array(full_s)
# ArrowInvalid: Could not convert <pyarrow.StringScalar: '50015202101011004687846'> with type pyarrow.lib.StringScalar: did not recognize Python value type when inferring an Arrow data type

h1_s = full_s.iloc[:len(full_s)//2].cat.remove_unused_categories()
pyarrow.array(h1_s)
# ArrowInvalid: Could not convert <pyarrow.StringScalar: '50015202101011004687846'> with type pyarrow.lib.StringScalar: did not recognize Python value type when inferring an Arrow data type

q1_s = h1_s.iloc[:len(h1_s)//2].cat.remove_unused_categories()
pyarrow.array(q1_s)
# works and creates a pyarrow.lib.DictionaryArray

q2_s = h1_s.iloc[len(h1_s)//2:].cat.remove_unused_categories()
pyarrow.array(q2_s)
# works and creates a pyarrow.lib.DictionaryArray

btw h1_s still has ~250mil rows so I can't provide that as a minimum example either.

[RabeezRiaz]

I've tested the above code on a string typed series full_s and there are no errors in all 4 tests (I get a pyarrow.lib.ChunkedArray in all 4).

[rhshadrach]

@RabeezRiaz - Yes, I understand that in this situation it may be difficult to come up with a reproducible example. However, if we are not able to reproduce the error, there isn't a whole lot that is able to be done. I would recommend trying different slices (other than just first half / second half).

[simonjayhawkins]

should probably close as can't reproduce.

[rhshadrach]

Agreed @simonjayhawkins; @RabeezRiaz if you can come up with a reproducible example, post it here and will be happy to reopen.