[Numpy-discussion] another view puzzle

[josef.pktd at gmail.com]

On Wed, Jun 3, 2009 at 5:55 PM, Robert Kern <robert.kern at gmail.com> wrote:
> On Wed, Jun 3, 2009 at 16:31,  <josef.pktd at gmail.com> wrote:
>> On Wed, Jun 3, 2009 at 5:18 PM, Christopher Barker
>> <Chris.Barker at noaa.gov> wrote:
>>> josef.pktd at gmail.com wrote:
>>>> Ok, I didn't know numpy can have structured matrices,
>>>
>>> well, matrices are a subclass of nd-arrays, so they support it, but it's
>>> probably not the least bit useful.
>>>
>>> See my earlier post to see how to do what I think you want.
>>>
>>> You may not want a matrix anyway -- a 2-d array may be a better bet. the
>>> only thing matrices buy you is convenient linear algebra operations.
>>
>> I'm very happy with plain numpy arrays, but to handle different data
>> types in scipy.stats, I'm still trying to figure out how views and
>> structured arrays work. And I'm still confused.
>
> .view() is used two different ways, and I think that is confusing you.
> .view(some_dtype) constructs a view of the array's memory with a
> different dtype. This can cause a reinterpretation of the bytes of
> memory. .view(ndarray_subclass) just returns an instance of
> ndarray_subclass that looks at the same array (same shape, dtype,
> etc.). This does not cause a reinterpretation of the memory.
>
> These are two completely different things, unfortunately conflated
> into the same method.

Thanks, this makes it much clearer than the current docstring for np.view().

I didn't even know about .view(ndarray_subclass) until Pierre
mentioned it today.

Do you have an opinion about whether  .view(ndarray_subclass) or
__array_wrap__ is the more appropriate return wrapper for function
such as the ones in stats?

Josef
>
> --
> 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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