[Numpy-discussion] A bug in numpy.random.shuffle?

[Jonathan Helmus]

On 09/05/2013 01:29 PM, Warren Weckesser wrote:
>
>
> On Thu, Sep 5, 2013 at 2:11 PM, Fernando Perez <fperez.net at gmail.com 
> <mailto:fperez.net at gmail.com>> wrote:
>
>     Hi all,
>
>     I just ran into this rather weird behavior:
>
>     http://nbviewer.ipython.org/6453869
>
>     In summary, as far as I can tell, shuffle is misbehaving when acting
>     on arrays that have structured dtypes. I've seen the problem on 1.7.1
>     (official on ubuntu 13.04) as well as master as of a few minutes ago.
>
>     Is this my misuse? It really looks like a bug to me...
>
>
>
> Definitely a bug:
>
> In [1]: np.__version__
> Out[1]: '1.9.0.dev-573b3b0'
>
> In [2]: z = np.array([(0,),(1,),(2,),(3,),(4,)], dtype=[('a',int)])
>
> In [3]: z
> Out[3]:
> array([(0,), (1,), (2,), (3,), (4,)],
>       dtype=[('a', '<i8')])
>
> In [4]: shuffle(z)
>
> In [5]: z
> Out[5]:
> array([(0,), (1,), (2,), (0,), (0,)],
>       dtype=[('a', '<i8')])
>
>
>
> Nothing in the docstring suggests that it shouldn't work for 
> structured dtypes.
>
> Warren

Looks to stemming from the fact that elements of records arrays cannot 
be swapped:

In [1]: import numpy as np

In [2]: x = np.zeros(5, dtype=[('n', 'S1'), ('i', int)])

In [3]: x['i'] = range(5)

In [4]: print x
[('', 0) ('', 1) ('', 2) ('', 3) ('', 4)]

In [5]: x[0], x[1] = x[1], x[0]

In [6]: print x
[('', 1) ('', 1) ('', 2) ('', 3) ('', 4)]

This is with numpy 1.7.1

Cheers,

     - Jonathan Helmus


>
>
>
>
>     Cheers,
>
>     f
>
>     --
>     Fernando Perez (@fperez_org; http://fperez.org)
>     fperez.net-at-gmail: mailing lists only (I ignore this when swamped!)
>     fernando.perez-at-berkeley: contact me here for any direct mail
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