Datetime / calendar histograms

[janpipek]

Requirements:

Possible axes:

1. month (cyclic)
2. year (continuous)
3. year+month (continuous)
4. day (continuous)
5. hour (cyclic)
6. weekday (cyclic)
7. week+weekday (continuous)
8. year + week (continuous) ...

Properties:

1. It must be possible to have a float quantity on other axes

Use case:

I have the following data:

2010-03-10, 4.3 deg
2010-03-11, -0.3 deg
...
2017-03-13, 3.4 deg
2017-03-14, 6.2 deg

I need a simple way to construct the histogram temperature vs. month of the year, ideally just calling h2...

Compatibility:

• must work with date, datetime objects
• must work with pandas internal and nat values

[janpipek]

Further requirements:

• enable merging
• enable flattening (year,month -> year+month