[Tutor] list to numpy record array

Vincent Davis vincent at vincentdavis.net
Tue Feb 23 18:58:38 CET 2010


@Skipper

Thanks I will post over on the scipy list

  *Vincent Davis
720-301-3003 *
vincent at vincentdavis.net
 my blog <http://vincentdavis.net> |
LinkedIn<http://www.linkedin.com/in/vincentdavis>


On Tue, Feb 23, 2010 at 10:55 AM, Skipper Seabold <jsseabold at gmail.com>wrote:

> On Mon, Feb 22, 2010 at 11:50 PM, Vincent Davis
> <vincent at vincentdavis.net> wrote:
> >
> > I must be missing something simple. I have a list of lists data = "[['
>  0', '  0', '234.0', '24.0', ' 25'], ['  1', '  0', '22428.0', '2378.1', '
> 25'],......" and what to make a record array from it but it gets screwed up
> or I don't get it, maybe both. Notice that at this stage the items are
> strings, not numbers, and there is whitespace not sure this matters.
> > Here is what is happening
> > adata = numpy.array(data,numpy.float64)
> >
> > >>> adata
> > array([[  0.00000000e+00,   0.00000000e+00,   2.34000000e+02,
> >           2.40000000e+01,   2.50000000e+01],
> >        ...,
> >        [  4.77000000e+02,   4.77000000e+02,   2.07000000e+02,
> >           4.58000000e+01,   2.50000000e+01]])
> >
> > This is what I would expect except it is not a record array.
> > This is not what I expect. I think I have tried every iteration including
> using numpy dtaypes numpy.int32 or bdata = numpy.array(data, dtype = [('x',
> int),('y', int),('mean',float),('stdv',float),('npixcels',int)])
> > What am I missing?
> >
> > bdata = numpy.array(data, [('x', int),('y',
> int),('mean',float),('stdv',float),('npixcels',int)])
> > >>> bdata
> > array([[(3153952, 0, 0.0, 0.0, 0), (3153952, 0, 0.0, 0.0, 0),
> >         (206933603122, 0, 0.0, 0.0, 0), (808334386, 0, 0.0, 0.0, 0),
> >         (3486240, 0, 0.0, 0.0, 0)],
> >        [(3219488, 0, 0.0, 0.0, 0), (3153952, 0, 0.0, 0.0, 0),
> >         (13561617777439282, 0, 0.0, 0.0, 0),
> >         (54074581398322, 0, 0.0, 0.0, 0), (3486240, 0, 0.0, 0.0, 0)],
> >        [(3285024, 0, 0.0, 0.0, 0), (3153952, 0, 0.0, 0.0, 0),
> >         (206933931058, 0, 0.0, 0.0, 0), (925775666, 0, 0.0, 0.0, 0),
> >         (3486240, 0, 0.0, 0.0, 0)],
> >        ...,
> >        [(3487540, 0, 0.0, 0.0, 0), (3618612, 0, 0.0, 0.0, 0),
> >         (206933602866, 0, 0.0, 0.0, 0), (908996661, 0, 0.0, 0.0, 0),
> >         (3486240, 0, 0.0, 0.0, 0)],
> >        [(3553076, 0, 0.0, 0.0, 0), (3618612, 0, 0.0, 0.0, 0),
> >         (13561596370041137, 0, 0.0, 0.0, 0),
> >         (62870573495603, 0, 0.0, 0.0, 0), (3486240, 0, 0.0, 0.0, 0)],
> >        [(3618612, 0, 0.0, 0.0, 0), (3618612, 0, 0.0, 0.0, 0),
> >         (206933798962, 0, 0.0, 0.0, 0), (942552372, 0, 0.0, 0.0, 0),
> >         (3486240, 0, 0.0, 0.0, 0)]],
> >
> >       dtype=[('x', '<i8'), ('y', '<i8'), ('mean', '<f8'), ('stdv',
> '<f8'), ('npixcels', '<i8')])
> >
> >
>
> I neglected to reply to the whole list on my first try.  For posterity's
> sake:
>
> You should ask on the scipy-user list with a self-contained example.
> It is heavily trafficked. http://www.scipy.org/Mailing_Lists
>
> From the example you gave above, I am not sure what's going unless
> it's something in the casting from strings.  Note though that you have
> created a structured array and not a record array.  The subtle
> difference is that the record array allows attribute lookup ie., you
> could do bdata.x instead of bdata['x'].  Structured arrays are usually
> faster as the attribute lookup convenience is implemented in Python
> whereas the structured arrays use C code.
>
> hth,
>
> Skipper
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/tutor/attachments/20100223/2fcbd4f1/attachment-0001.html>


More information about the Tutor mailing list