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

[Charles R Harris]

On Thu, Sep 5, 2013 at 1:34 PM, Bradley M. Froehle
<brad.froehle at gmail.com>wrote:

> I put this test case through `git bisect run` and here's what came
> back.  I haven't confirmed this manually yet, but the blamed commit
> does seem reasonable:
>
> b26c675e2a91e1042f8f8d634763942c87fbbb6e is the first bad commit
> commit b26c675e2a91e1042f8f8d634763942c87fbbb6e
> Author: Nathaniel J. Smith <njs at pobox.com>
> Date:   Thu Jul 12 13:20:20 2012 +0100
>
>     [FIX] Make np.random.shuffle less brain-dead
>
>     The logic in np.random.shuffle was... not very sensible. Fixes trac
>     ticket #2074.
>
>     This patch also exposes a completely unrelated issue in
>     numpy.testing. Filed as Github issue #347 and marked as knownfail for
>     now.
>
> :040000 040000 6f3cf0c85a64664db6a71bd59909903f18b51639
> 0b6c8571dd3c9de8f023389f6bd963e42b12cc26 M numpy
> bisect run success
>
> On Thu, Sep 5, 2013 at 11:58 AM, Charles R Harris
> <charlesr.harris at gmail.com> wrote:
> >
> >
> >
> > On Thu, Sep 5, 2013 at 12:50 PM, Fernando Perez <fperez.net at gmail.com>
> > wrote:
> >>
> >> On Thu, Sep 5, 2013 at 11:43 AM, Charles R Harris
> >> <charlesr.harris at gmail.com> wrote:
> >>
> >>
> >> > Oh, nice one ;) Should be fixable if you want to submit a patch.
> >>
> >> Strategy? One option is to do, for structured arrays, a shuffle of the
> >> indices and then an in-place
> >>
> >> arr = arr[shuffled_indices]
> >>
> >> But there may be a cleaner/faster way to do it.
> >>
> >> I'm happy to submit a patch, but I'm not familiar enough with the
> >> internals to know what the best approach should be.
> >>
> >
> > Better open an issue. It looks like a bug in the indexing code.
> >
>

Also fails for string arrays.

In [6]: x = np.zeros(5, dtype=[('n', 'S1'), ('s', 'S1')])

In [7]: x['s'] = [c for c in 'abcde']

In [8]: x
Out[8]:
array([('', 'a'), ('', 'b'), ('', 'c'), ('', 'd'), ('', 'e')],
      dtype=[('n', 'S1'), ('s', 'S1')])

In [9]: x[0], x[1] = x[1], x[0]

In [10]: x
Out[10]:
array([('', 'b'), ('', 'b'), ('', 'c'), ('', 'd'), ('', 'e')],
      dtype=[('n', 'S1'), ('s', 'S1')])

Chuck
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