Add indexName to DataFrame.to_json(orient='split')

[Suor]

Code Sample, a copy-pastable example if possible

import pandas as pd

df = pd.DataFrame([[1,2,3],[4,5,6]], columns=['a','b','c'])
df.index = df.a
df_copy = pd.io.read.read_json(df.to_json(orient='split'), orient='split')
assert df_copy.index.name == df.index.name

Problem description

I use .to_json(orient='split') as a compact way to serialize and store dataframes, however, I loose index name on dump/load cycle. I would suggest adding "indexName" to json, which should be fairly backwards compatible.

Expected Output

>>>  df.to_json(orient='split')
'{"columns":["a","b","c"],"index":[1,4],"indexName":"a","data":[[1,2,3],[4,5,6]]}'

Behavior should probably stay as it is when index name is None.

Output of pd.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 2.7.13.final.0 python-bits: 64 OS: Linux OS-release: 4.10.0-28-generic machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: en_US.UTF-8

pandas: 0.20.3
pytest: 2.6.4
pip: 9.0.1
setuptools: 36.2.5
Cython: None
numpy: 1.13.1
scipy: 0.16.0
xarray: None
IPython: 5.4.1
sphinx: None
patsy: 0.4.1
dateutil: 2.6.1
pytz: 2017.2
blosc: None
bottleneck: None
tables: None
numexpr: 2.6.2
feather: None
matplotlib: None
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
sqlalchemy: None
pymysql: None
psycopg2: 2.6 (dt dec pq3 ext lo64)
jinja2: 2.7.3
s3fs: None
pandas_gbq: None
pandas_datareader: None

[jreback]

this makes the JSON pretty pandas specific, so really not in favor of this you can simply .reset_index() and make it a column.

[Suor]

This makes dataframe fully recoverable from json. Also, it's already specific since there is both columns and index, and anyone can ignore it, so don't see an issue here.

[WillAyd]

I think this is realistically already achievable with the table orient, so unlikely to add to split