[Numpy-discussion] Python scalar float indices into array work - but not for array indices - why ?

Robert Kern robert.kern@gmail....
Wed Nov 17 13:15:44 CST 2010


On Wed, Nov 17, 2010 at 13:11, Sebastian Haase <seb.haase@gmail.com> wrote:
> On Wed, Nov 17, 2010 at 7:48 PM, Nathaniel Smith <njs@pobox.com> wrote:
>> On Wed, Nov 17, 2010 at 10:32 AM, Sebastian Haase <seb.haase@gmail.com> wrote:
>>> On Wed, Nov 17, 2010 at 7:26 PM, Robert Kern <robert.kern@gmail.com> wrote:
>>>> On Wed, Nov 17, 2010 at 12:20, Sebastian Haase <seb.haase@gmail.com> wrote:
>>>>> Why does numpy not accept float arrays as indices ?
>>>>> I was very happy and quite surprised once I found out that it worked
>>>>> at all for Python float scalars,
>>>>> but would it not just be consequent to also allow float ndarrays then ?
>>>>
>>>> It only works for float scalars by accident. Do not rely on it.
>>>
>>> Could you be more specific ?  As a feature, it for sure can be useful.
>>
>> I think Robert Kern has the same intuition as me: that supporting
>> float indices is pointless. So, can you give any *specific examples*
>> of things you can do with float indices that would be difficult or
>> more expensive using integer indices? That's probably the best way to
>> convince people.
>>
>> -- Nathaniel
> Well,
> suppose you have 2 vectors of floating point coordinates `x` and `y`
> and you want to do operations utilizing fancy indexing like
> image[ [x,y] ] +=  1
>
> As I just realized, this specific case seems to be addressed by histogram2d,
> however, if float indices would work this would of course be much more
> general: higher dimensionality and not just '+=' operations.

Actually, it wouldn't work even if x and y were integers.

-- 
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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