Hi Pierre, On Monday 04 August 2008 04:29:57 pm Pierre GM wrote: > On Monday 04 August 2008 14:16:33 Darren Dale wrote: > > Hi Jarrod, > > > > I was wondering if someone knowledgeable would please look into the > > behavior of concatenate() with subclasses of ndarray. > > Darren, > I ran into similar problems when I started working on numpy.ma and > scikits.timeseries, and I remember having conversations with Bryce Hendrix > of Enthought about that on this very list. > > I think you have a problem in `NDQuantities.__array_finalize__`: you don't > initialize `._units` if `obj` doesn't have a `_units`. At least, you should > use something like > self._units = getattr(obj, '_units', None), > which will set `._units` to None if `obj` is not a NDQuantities, and will > also ensure that your NDQuantities array always have a ._units attribute. > In other words, if I take a view of a ndarray as a NDQuantities, I should > have a _units defined by default (None being the most appropriate in that > case). > > About concatenation: > In a lot of cases, concatenate requires some tweaking. In > scikits.timeseries, we have to decide what to do when the series being > concatenated overlap. In your case, you have to decide what to do when > concatenating 2 arrays A & B, for example: > * if A & B have the same unit, keep it > * If A (B) doesn't have a unit, keep the unit of B (A) > * If the units of A and B are compatible, convert one to the other > * If the units are incompatible, raise an exception. > What I suggest is to implement your own concatenate: check the units, > concatenate the arrays as regular ndarrays, take a view of the result, > modify the unit of the result accordingly. > > About subclassing: > * You may want to check the cookbook: > http://www.scipy.org/Subclasses > * You may also want to check other ndarray subclasses, such as MaskedArray, > TimeSeries (</pushing product>) for some implementation details. > * You may also want add your own experience on > http://www.scipy.org/Subclasses, so that we don't lose it. > > Drop me a line offlist if you'd like, I'd be happy to help (depending on > the time at hand). > Cheers.
Thank you for the comments. You made a number of good points and I will look into each. I agree that it looks like I need to write my own concatenate function, but judging from Travis' comment a while back, there may still be an issue with numpy's concatenate. In my example, it is not just that concat is stripping the units, it is returning a different type. Maybe that is not such a bad thing in this case, but I thought it should be brought to the numpy maintainers attention. Darren _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
