On Thu, 2012-11-22 at 16:05 +0100, Daπid wrote: > On Thu, Nov 22, 2012 at 3:54 PM, <[email protected]> wrote: > > Why don't operations on empty arrays not return empty arrays? > > Because functions like mean or std are expected to return a scalar. > Functions that are piecewiese can (and should) return an empty array, > but not the mean.
I agree, this makes sense, note that: In [2]: a = np.empty((5,0)) In [3]: a.std(0) Out[3]: array([], dtype=float64) In [4]: a.std(1) /usr/bin/ipython:1: RuntimeWarning: invalid value encountered in divide #!/usr/bin/env python Out[4]: array([ nan, nan, nan, nan, nan]) However you are reducing, and with reducing you expect exactly 1 scalar result (along that dimension). > _______________________________________________ > NumPy-Discussion mailing list > [email protected] > http://mail.scipy.org/mailman/listinfo/numpy-discussion > _______________________________________________ NumPy-Discussion mailing list [email protected] http://mail.scipy.org/mailman/listinfo/numpy-discussion
