[Numpy-discussion] Documentation for dtypes with named fields

[Skipper Seabold]

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.

Skipper