Description
-
I have checked that this issue has not already been reported.
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I have confirmed this bug exists on the latest version of pandas.
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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