[Numpy-discussion] Logical indexing and higher-dimensional arrays.

Robert Kern robert.kern@gmail....
Wed Feb 8 16:19:03 CST 2012


On Wed, Feb 8, 2012 at 22:11, Travis Oliphant <travis@continuum.io> wrote:
>
> On Feb 8, 2012, at 11:17 AM, josef.pktd@gmail.com wrote:
>
>> On Wed, Feb 8, 2012 at 10:29 AM, Sturla Molden <sturla@molden.no> wrote:
>>> On 08.02.2012 15:49, Travis Oliphant wrote:
>>>
>>>> This sort of thing would take time, but is not out of the question in my mind because I suspect the number of users and use-cases of "broadcasted" fancy-indexing is small.
>>
>> I think I use it quite a bit, and I like that the broadcasting in
>> indexing is as flexible as the broadcasting of numpy arrays
>> themselves.
>>
>> x[np.arange(len(x)), np.arange(len(x))]  gives the diagonal for example.
>>
>> or picking a different element from each column, (I don't remember
>> where I used that)
>>
>> It is surprising at first and takes some getting used to, but I think
>> it's pretty nice.  On the other hand, I always avoid mixing slices and
>> indexes because of "strange" results.
>
> It actually is pretty nice once you understand it.   Mixing of fancy indexing and slicing is only nice in special circumstances.   I think we would have been better off if rather than move the subspace to the beginning of the array, NumPy raised an error in that case.
>
> That would be a useful change.

We could start with a warning. See how many people kvetch about it. I
don't like removing long-standing, documented features based on
suspicions that their user base is small. Our suspicions and
intuitions about such things aren't worth much.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
  -- Umberto Eco


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