Feature request: Python tools for obs sequences

[hkershaw-brown]

Use case

For CROCODILE, Python based tools for observation space diagnostics. Might be useful more generally for DART, so adding this issue to track.

Is your feature request related to a problem?

Originally for CROCODILE obs space diaginostic plotting in the python ecosystem, but the ability to examine obs squences in a dataframe in a Jupyter notebook (or Python tool of your choice) is quite helpful, e.g. finding duplicates in obs sequences, looking at output from obs converters, subsetting observations (in space, time, or by X), splitting and joining obs sequences.
No need to run obs_diag to bin observations, you can read the obs_sequence into a dataframe directly.

Example finding duplicates:

Describe your preferred solution

https://github.com/NCAR/pyDARTdiags. See issues for various notes and docs for documentation.
https://pypi.org/project/pydartdiags/ (but recommend you do a local editable pip install if you are developing this or playing with it)
BUYER BEWARE, this is bleeding edge.

Describe any alternatives you have considered

Currently using pandas, which seems ok (tried naively loading 20GB obs sequences one after the other, actually worked on my mac). Probably need to think about big-big data tools for going larger (and maybe faster).
Also keeping notes on other observation tools (NCAR/pyDARTdiags#4).