[Numpy-discussion] the mean, var, std of empty arrays
Sebastian Berg
sebastian@sipsolutions....
Thu Nov 22 09:15:54 CST 2012
On Thu, 2012-11-22 at 16:05 +0100, Daπid wrote:
> On Thu, Nov 22, 2012 at 3:54 PM, <josef.pktd@gmail.com> 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
> NumPy-Discussion@scipy.org
> http://mail.scipy.org/mailman/listinfo/numpy-discussion
>
More information about the NumPy-Discussion
mailing list