[Numpy-discussion] Datetime branch
Thu Jun 11 14:37:20 CDT 2009
On Jun 11, 2009, at 3:07 PM, Travis Oliphant wrote:
>> BTW, what is the metadata that is going to be added to the types?
>> What purpose does it serve?
> In the date-time case, it holds what frequency the integer in the
> type represents. There will only be 2 new static data-types.
> "Datetime" and "Timedelta" that use 8 bytes each.
> What those 8 bytes represent will be determined by the metadata
> (years, months, seconds, etc...).
As Charles pointed out, it'd be quite useful for units as well. Or to
store some extra information like the filling_value of a MaskedArray...
So, this metadata would be attached to an array, right ? Scalars would
be considered as 0d array for that purpose, right ? eg, given a 1d
array of dates w/ a given frequency, accessing a single element would
give me a scalar w/ the same frequency ?
> The ufunc machinery needs to change to handle passing
> that information in somehow. The approaches we take to doing that
> will also hopefully allow us to define ufuncs for string, unicode, and
> void * arrays as well.
In that case, could we also think about what Darren was suggesting for
his units package, viz, a pre-processing function (__array_unwrap__ ?)
that complements the current __array_wrap__ one ? The idea being that
any operation would be performed on a ndarray, the corresponding
metadata would be just passed along during the operation, and
modifications to the metadata would be taken care of in the pre- and/
or post- processing steps ?
Oh, just another question: why trying to put datetime and timedelta in
the type ordering ? My understanding is that underneath, they're just
long/longlong. It's only because they have a particular metadata that
they should be processed differently, right ? So, if soon we add units
to floats, the underneath object would still be considered float,
dealing w/ the unit has to be let for ufuncs ?
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