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BUG: PeriodIndex does not survive JSON serialization roundtrip #44720

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jmg-duarte opened this issue Dec 2, 2021 · 1 comment · Fixed by #47747
Closed
3 tasks done

BUG: PeriodIndex does not survive JSON serialization roundtrip #44720

jmg-duarte opened this issue Dec 2, 2021 · 1 comment · Fixed by #47747
Labels
Bug Dtype Conversions Unexpected or buggy dtype conversions IO JSON read_json, to_json, json_normalize Period Period data type

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@jmg-duarte
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jmg-duarte commented Dec 2, 2021

  • 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 master branch of pandas.

Reproducible Example

import pandas as pd
df = pd.DataFrame(
  {"column": range(10, 20, 2)},
  index=pd.PeriodIndex(
    year=[2020, 2020, 2020, 2020, 2021], quarter=[1, 2, 3, 4, 1]
  ),
)

df_from_json = pd.read_json(df.to_json(orient='table'), orient='table')
assert df.equals(df_from_json)

Issue Description

The index should make the roundtrip.

Possible related issue: #32665

Expected Behavior

From my point of view, this issue has two parts, the title and example report on the overall issue which is the failure to roundtrip the index when using JSON to serialize the DataFrame.

The second part of the issue is that when reading from JSON, the index gets serialized to a DatetimeIndex with freq=None.
In the JSON however, the frequency is there, see the output of df.to_json(orient='table') for the previous example:

{'data': [{'column': 10, 'index': '2020-01-01T00:00:00.000Z'},
          {'column': 12, 'index': '2020-04-01T00:00:00.000Z'},
          {'column': 14, 'index': '2020-07-01T00:00:00.000Z'},
          {'column': 16, 'index': '2020-10-01T00:00:00.000Z'},
          {'column': 18, 'index': '2021-01-01T00:00:00.000Z'}],
 'schema': {'fields': [{'freq': 'Q-DEC', 'name': 'index', 'type': 'datetime'},
                       {'name': 'column', 'type': 'integer'}],
            'pandas_version': '0.20.0',
            'primaryKey': ['index']}}

Notice how the index field has the freq correctly set.

Installed Versions

INSTALLED VERSIONS
------------------
commit           : 945c9ed766a61c7d2c0a7cbb251b6edebf9cb7d5
python           : 3.8.5.final.0
python-bits      : 64
OS               : Darwin
OS-release       : 20.6.0
Version          : Darwin Kernel Version 20.6.0: Wed Jun 23 00:26:31 PDT 2021; root:xnu-7195.141.2~5/RELEASE_X86_64
machine          : x86_64
processor        : i386
byteorder        : little
LC_ALL           : None
LANG             : en_GB.UTF-8
LOCALE           : en_GB.UTF-8

pandas : 1.3.4
numpy : 1.21.3
pytz : 2021.3
dateutil : 2.8.2
pip : 21.3.1
setuptools : 58.3.0
Cython : None
pytest : 6.2.5
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : 1.1
pymysql : None
psycopg2 : None
jinja2 : None
IPython : 7.30.0
pandas_datareader: None
bs4 : None
bottleneck : None
fsspec : None
fastparquet : None
gcsfs : None
matplotlib : None
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : 5.0.0
pyxlsb : None
s3fs : None
scipy : None
sqlalchemy : 1.4.26
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
numba : None

@jmg-duarte jmg-duarte added Bug Needs Triage Issue that has not been reviewed by a pandas team member labels Dec 2, 2021
@mroeschke mroeschke added Dtype Conversions Unexpected or buggy dtype conversions IO JSON read_json, to_json, json_normalize Period Period data type and removed Needs Triage Issue that has not been reviewed by a pandas team member labels Dec 27, 2021
@jmg-duarte
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I have a fix for this. I'm just trying to setup pandas in development mode on my computer and failing (see #47737).

I've also tried regular pip but pandas requires pg_config for some reason?

Is there a way I can avoid setting up the more complex parts of the development environment so I can just test the JSON part?

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Labels
Bug Dtype Conversions Unexpected or buggy dtype conversions IO JSON read_json, to_json, json_normalize Period Period data type
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