Pandas: add indent support to `to_json` method

[phretor]

Sometimes you just want to have a quick look at your data in IPython and having to_json to support indent (as both json.dumps and simplejson.dumps do) would be very handy.

A workaround, which however doesn't always work, is to do json.dumps(series.to_dict()), which unfortunately is annoying when you don't have a JSON-serializable type (e.g., numpy.bool_).

I'm leaving this here as a food for discussion.

[ludaavics]

Another workaround: df_json_pretty = json.dumps(json.loads(df.to_json()), indent=2)

[devforfu]

Is it still on the list to be implemented?

[TomAugspurger]

Still open. Feel free to work on it if you want, but the current json isn't the friendliest.

[devforfu]

@TomAugspurger Ok, got it! I'll try to figure out if there is a straightforward way to deal with it.

[kylebarron]

It looks like the JSON writer uses Pandas' own JSON writer:
https://github.com/pandas-dev/pandas/blob/011b79fbf73b45313b47c08b4be1fc07dcb99365/pandas/io/json/json.py#L7

It looks like eventually it calls objToJSON in C here:
https://github.com/pandas-dev/pandas/blob/011b79fbf73b45313b47c08b4be1fc07dcb99365/pandas/_libs/src/ujson/python/objToJSON.c#L2317-L2321

So if I'm not mistaken, to add an indent option, you'd need to change the C code?

[TomAugspurger]

Yep that sounds right. FYI, I think ripping out that JSON code and
replacing it with something more maintainable
(maybe based on Apache Arrow's JSON support) is on the medium to long-term
agenda.

On Mon, Nov 12, 2018 at 9:28 AM Kyle Barron [e-mail]
wrote:

It looks like the JSON writer
https://github.com/pandas-dev/pandas/blob/011b79fbf73b45313b47c08b4be1fc07dcb99365/pandas/io/json/json.py#L107-L117
uses Pandas' own JSON writer:

https://github.com/pandas-dev/pandas/blob/011b79fbf73b45313b47c08b4be1fc07dcb99365/pandas/io/json/json.py#L7

It looks like eventually it calls objToJSON in C here:

https://github.com/pandas-dev/pandas/blob/011b79fbf73b45313b47c08b4be1fc07dcb99365/pandas/_libs/src/ujson/python/objToJSON.c#L2317-L2321

So if I'm not mistaken, to add an indent option, you'd need to change the
C code?

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[kylebarron]

Is the current JSON writer believed to be much faster than the Python standard library's JSON writer?

[TomAugspurger]

Yep. It also handles types not supported by the stdlib's json writer
(notably numpy types).

On Mon, Nov 12, 2018 at 9:55 AM Kyle Barron [e-mail]
wrote:

Is the current JSON writer believed to be much faster than the Python
standard library's JSON writer?

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[botenvouwer]

I agree on this, JSON is also meant to be human readable. Right now this is just annoying.