[Numpy-discussion] Does x[True] trigger basic or advanced indexing?
Eric Wieser
wieser.eric+numpy at gmail.com
Thu Dec 14 11:24:09 EST 2017
It sounds like you're using an old version of numpy, where boolean scalars
were interpreted as integers.
What version are you using?
Eric
On Thu, Dec 14, 2017, 04:27 Joe <solarjoe at posteo.org> wrote:
> Hello,
> thanks for you feedback.
>
> Sorry, if thie question is stupid and the case below does not make
> sense.
> I am just trying to understand the logic.
> For
>
> x = np.random.rand(2,3)
>
> x[True]
> x[(True,)]
>
> or
>
> x[False]
> x[(False,)]
>
> where True and False are not arrays,
> it will pick the first or second row.
>
> Is this basic indexing then with one the rules
> - obj is an integer
> - obj is a tuple of slice objects and integers.
> ?
>
>
> Am 13.12.2017 21:49 schrieb Eric Wieser:
> > Increasingly, NumPy does not considers booleans to be integer types,
> > and indexing is one of these cases.
> >
> > So no, it will not be treated as a tuple of integers, but as a 0d mask
> >
> > Eric
> >
> > On Wed, 13 Dec 2017 at 12:44 Joe <solarjoe at posteo.org> wrote:
> >
> >> Hi,
> >>
> >> yet another question.
> >>
> >> I looked through the indexing rules in the
> >> documentation but I count not find which one
> >> applies to x[True] and x[False]
> >>
> >> that might e.g result from
> >>
> >> import numpy as np
> >> x = np.array(3)
> >> x[x>5]
> >> x[x<1]
> >> x[True]
> >> x[False]
> >>
> >> x = np.random.rand(2,3)
> >> x[x>5]
> >> x[x<1]
> >> x[True]
> >> x[False]
> >>
> >> I understood that they are equivalent to
> >>
> >> x[(False,)]
> >>
> >> I tested it and it looks like advanced indexing,
> >> but I try to unterstand the logic behind this,
> >> if there is any :)
> >>
> >> In x[x<1] the x<1 is a mask and thus I guess it is a
> >> "tuple with at least one sequence object or ndarray (of data type
> >> integer or bool)", right?
> >>
> >> Or will x[True] trigger basic indexing as it is "a tuple of
> >> integers"
> >> because True will be converted to Int?
> >>
> >> Cheers,
> >> Joe
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> >
> >
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