[Numpy-discussion] Dates and times and Datetime64 (again)

[Chris Barker]

On Fri, Apr 11, 2014 at 4:58 PM, Stephan Hoyer <shoyer at gmail.com> wrote:

> On Fri, Apr 11, 2014 at 3:56 PM, Charles R Harris <
> charlesr.harris at gmail.com> wrote:
>
>> Are we in a position to start looking at implementation? If so, it would
>> be useful to have a collection of test cases, i.e., typical uses with
>> specified results. That should also cover conversion from/(to?)
>> datetime.datetime.
>>
>
yup -- tests are always good!

Indeed, my personal wish-list for np.datetime64 is centered much more on
> robust conversion to/from native date objects, including comparison.
>

A good use case.


>  Here are some of my particular points of frustration (apologies for the
> thread jacking!):
> - NaT should have similar behavior to NaN when used for comparisons (i.e.,
> comparisons should always be False).
>

make sense.


>  - You can't compare a datetime object to a datetime64 object.
>

that would be nice to have.


> - datetime64 objects with high precision (e.g., ns) can't compare to
> datetime objects.
>

That's a problem, but how do you think it should be handled? My thought is
that it should round to microseconds, and then compare -- kind of like
comparing float32 and float64...


> Pandas has a very nice wrapper around datetime64 arrays that solves most
> of these issues, but it would be nice to get much of that functionality in
> core numpy,
>

yes -- it would -- but learning from pandas is certainly a good idea.

>
> from numpy import datetime64
> from datetime import datetime
>
> print np.datetime64('NaT') < np.datetime64('2011-01-01') # this should not
> to true
> print datetime(2010, 1, 1) < np.datetime64('2011-01-01') # raises exception
> print np.datetime64('2011-01-01T00:00', 'ns') > datetime(2010, 1, 1) #
> another exception
> print np.datetime64('2011-01-01T00:00') > datetime(2010, 1, 1) # finally
> something works!
>
>
now to get them into proper unit tests....

-CHB


-- 

Christopher Barker, Ph.D.
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