[Numpy-discussion] Documentation for dtypes with named fields
josef.pktd at gmail.com
josef.pktd at gmail.com
Tue Mar 16 12:08:37 EDT 2010
On Tue, Mar 16, 2010 at 11:52 AM, Skipper Seabold <jsseabold at gmail.com> wrote:
> On Tue, Mar 16, 2010 at 11:46 AM, <josef.pktd at gmail.com> wrote:
>> On Tue, Mar 16, 2010 at 11:34 AM, Skipper Seabold <jsseabold at gmail.com> wrote:
>>> On Tue, Mar 16, 2010 at 11:20 AM, Sam Tygier
>>> <Sam.Tygier at 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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