On Tue, Nov 6, 2012 at 7:52 PM, Warren Weckesser wrote: On Tue, Nov 6, 2012 at 8:27 PM, Phillip Feldman <
phillip.m.feldman@gmail.com> wrote: numpy.unique behaves as I would expect for small inputs like the
following: In [12]: x= [0, 0, 1, 0, 1, 2, 0, 1, 2, 3] In [13]: unique(x, return_index=True)
Out[13]: (array([0, 1, 2, 3]), array([0, 2, 5, 9], dtype=int64)) But, when I give it something larger, the return index values do not
always correspond to the first occurrences in the input. The documentation
is silent on the question of how the return index values are chosen when a
given element of x appears more than once. Either the documentation should
be
clarified, or better yet, the behavior should be changed. In fact, it was changed (in the master branch on github) several months
ago, but there has not yet been a release with the changes. The sort
method that np.unique passes to np.argsort is now 'mergesort', and the
docstring states that the indices returned are for the first occurrences of
the unique elements. The new docstring is here:
http://docs.scipy.org/doc/numpy-dev/reference/generated/numpy.unique.html#nu... See
https://github.com/numpy/numpy/commit/dbf235169ed3386b359caaa9217f5280bf1d67... the commit, and
https://github.com/numpy/numpy/blob/master/numpy/lib/arraysetops.py for
the latest version of the source. That change was backported to 1.6.2, but doesn't work for record/object
arrays. That oversight is fixed in master.
Chuck