[Numpy-discussion] BOF notes: Fernando's proposal: NumPy ndarray with named axes

[Rob Speer]

Keith Goodman wrote:
> I ran into a few more questions while playing with datarrays, so I started a list:
> http://github.com/kwgoodman/datarrayQ

I have quick answers to some of the questions.

> Can I have ticks without labels?
Ideally, yes, but good catch: the current code disallows that for no
good reason.

> Add a ticks input parameter?
I very much approve of this proposal (to add ticks= to define ticks
separately from axes).

> Create Axis._tick_dict when needed?
Wait, the dictionary wouldn't be saved at all? What's the point, then?
Constant-time lookups of tick names are essential, and this proposal
would turn that into linear time.

> Can we prevent user from messing up a datarray?
No. That's pretty much built into Python: the downstream user can do
anything they want to.
Our job is to make sure that what the user wants to do is use the
datarray correctly. :)

> 0d datarrays?
As 0d datarrays are completely pointless, I'm pretty sure that any
code that creates a 0d datarray is a mistake and should fail early.

> Can axis labels be anything besides None or str?
Possibly. The part of this question I particularly like is accessing
attributes programmatically, using arr.axis[axisname]. That gives
.axis much more of a purpose. (Follow-up question: should we merge
.axis and .axes in the API?)

> Direct access to array?
It's trivial: DataArray is a subclass of ndarray, so a DataArray
already is an ndarray. If you want to strip off all the datarray stuff
anyway (perhaps for efficiency reasons), you can use np.asarray(arr).

> Support for alignment?
Very yes. Aligning/joining labels is something that basically everyone
who works with labeled data needs to do, so we should figure out the
logic for it and include it in datarray so downstream users don't have
to reinvent it.

> Can labels and ticks be changed?
I'd favor them being immutable, but could have my mind changed by a
good use case for mutating them.

-- Rob