[Numpy-discussion] Documentation for dtypes with named fields

josef.pktd@gmai... josef.pktd@gmai...
Tue Mar 16 11:08:37 CDT 2010


On Tue, Mar 16, 2010 at 11:52 AM, Skipper Seabold <jsseabold@gmail.com> wrote:
> On Tue, Mar 16, 2010 at 11:46 AM,  <josef.pktd@gmail.com> wrote:
>> On Tue, Mar 16, 2010 at 11:34 AM, Skipper Seabold <jsseabold@gmail.com> wrote:
>>> On Tue, Mar 16, 2010 at 11:20 AM, Sam Tygier
>>> <Sam.Tygier@hep.manchester.ac.uk> wrote:
>>>> Thanks for those responses.
>>>>
>>>> could the dtype pages in the numpy reference link to the basics.rec page in the user guide?
>>>>
>>>> there seem to be some gotchas in list within a list notation.
>>>>
>>>> if i have
>>>> a = array([0,0.1,0.2,0.3,0.4])
>>>> b =  array((0,0.1,0.2,0.3,0.4), dtype=[('a','f'), ('b','f'), ('c','f'), ('d','f'),('f','f')])
>>>>
>>>> then
>>>>>>> a[[0,1,4]]
>>>> array([ 0. ,  0.1,  0.4])
>>>>>>> a[[4,1,0]]
>>>> array([ 0.4,  0.1,  0. ])
>>>>
>>>> but
>>>>>>> b[['a','b','f']]
>>>> (0.0, 0.10000000149011612, 0.40000000596046448)
>>>>>>> b[['f','b','a']]
>>>> (0.0, 0.10000000149011612, 0.40000000596046448)
>>>>
>>>> so i always get the vales back in the original order. is the by design, or a bug?
>>>>
>>>
>>> I've been bitten by this before too and asked the same question with
>>> no response.  I think it's just a limitation of the design of
>>> structured arrays.
>>
>> It might be by historical design, structured arrays are not really
>> designed for slicing but I think more like sets of variables.
>>
>> But it means it cannot be used directly for the old pattern
>>
>> [arr(name) for name in listofnames]
>>
>> Skipper, Is this subset selection documented anywhere? I only know
>> about it because you showed the example.
>>
>
> Just added it and a link to the cookbook for recarrays.  I don't think
> it will show up until the doc wiki changes are applied(?).
>
> http://docs.scipy.org/numpy/docs/numpy.doc.structured_arrays/

looks good, together with the cookbook on .view() it almost covers the
FAQs for structured arrays

I changed "OK to apply:" to  Yes  so it will get into the docs soon

Josef
>
> Skipper
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