On Do, 2015-06-04 at 18:04 -0700, Nathaniel Smith wrote:
> On Thu, Jun 4, 2015 at 5:57 PM, Nathaniel Smith <n...@pobox.com> wrote:
> > So specifically the question is -- if you have an array with five
> items, and
> > a Boolean array with three items, then currently you can use the
> later to
> > index the former:
> >
> > arr = np.arange(5)
> > mask = np.asarray([True, False, True])
> > arr[mask] # returns array([0, 2])
> >
> > This is justified by the rule that indexing with a Boolean array
> should be
> > the same as indexing with the same array that's been passed to
> np.nonzero().
> > Empirically, though, this causes constant confusion and does not
> seen very
> > useful, so the question is whether we should deprecate it.
>
> One place where the current behavior is particularly baffling and
> annoying is when you have multiple boolean masks in the same indexing
> operation. I think everyone would expect this to index separately on
> each axis ("outer product indexing" style, like slices do), and that's
> really the only useful interpretation, but that's not what it does...:This is not being deprecated in there for the moment, it is a different discussion. Though maybe we can improve the error message to mention that the array was originally boolean, has always been bugging me a bit (it used to mention for some cases it is not anymore). - Sebastian > In [3]: a = np.arange(9).reshape((3, 3)) > > In [4]: a > Out[4]: > array([[0, 1, 2], > [3, 4, 5], > [6, 7, 8]]) > > In [6]: a[np.asarray([True, False, True]), np.asarray([False, True, > True])] > Out[6]: array([1, 8]) > > In [7]: a[np.asarray([True, False, True]), np.asarray([False, False, > True])] > Out[7]: array([2, 8]) > > In [8]: a[np.asarray([True, False, True]), np.asarray([True, True, > True])] > --------------------------------------------------------------------------- > IndexError Traceback (most recent call > last) > <ipython-input-8-30b3427bec2a> in <module>() > ----> 1 a[np.asarray([True, False, True]), np.asarray([True, True, > True])] > > IndexError: shape mismatch: indexing arrays could not be broadcast > together with shapes (2,) (3,) > > > -n > > -- > Nathaniel J. Smith -- http://vorpus.org > _______________________________________________ > NumPy-Discussion mailing list > NumPy-Discussion@scipy.org > http://mail.scipy.org/mailman/listinfo/numpy-discussion
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