[Numpy-discussion] add axis to results of reduction (mean, min, ...)
josef.pktd@gmai...
josef.pktd@gmai...
Mon Aug 10 11:10:05 CDT 2009
On Mon, Aug 10, 2009 at 11:55 AM, Keith Goodman<kwgoodman@gmail.com> wrote:
> On Thu, Aug 6, 2009 at 9:07 AM, Robert Kern<robert.kern@gmail.com> wrote:
>> On Thu, Aug 6, 2009 at 11:03, Keith Goodman<kwgoodman@gmail.com> wrote:
>>> On Thu, Aug 6, 2009 at 8:55 AM, <josef.pktd@gmail.com> wrote:
>>>> What's the best way of getting back the correct shape to be able to
>>>> broadcast, mean, min,.. to the original array, that works for
>>>> arbitrary dimension and axis?
>>>>
>>>> I thought I have seen some helper functions, but I don't find them anymore?
>>>>
>>>> Josef
>>>>
>>>>>>> a
>>>> array([[1, 2, 3, 3, 0],
>>>> [2, 2, 3, 2, 1]])
>>>>>>> a-a.max(0)
>>>> array([[-1, 0, 0, 0, -1],
>>>> [ 0, 0, 0, -1, 0]])
>>>>>>> a-a.max(1)
>>>> Traceback (most recent call last):
>>>> File "<pyshell#135>", line 1, in <module>
>>>> a-a.max(1)
>>>> ValueError: shape mismatch: objects cannot be broadcast to a single shape
>>>>>>> a-a.max(1)[:,None]
>>>> array([[-2, -1, 0, 0, -3],
>>>> [-1, -1, 0, -1, -2]])
>>>
>>> Would this do it?
>>>
>>>>> pylab.demean??
>>> Type: function
>>> Base Class: <type 'function'>
>>> String Form: <function demean at 0x3c5c050>
>>> Namespace: Interactive
>>> File: /usr/lib/python2.6/dist-packages/matplotlib/mlab.py
>>> Definition: pylab.demean(x, axis=0)
>>> Source:
>>> def demean(x, axis=0):
>>> "Return x minus its mean along the specified axis"
>>> x = np.asarray(x)
>>> if axis:
>>> ind = [slice(None)] * axis
>>> ind.append(np.newaxis)
>>> return x - x.mean(axis)[ind]
>>> return x - x.mean(axis)
>>
>> Ouch! That doesn't handle axis=-1.
>>
>> if axis != 0:
>> ind = [slice(None)] * x.ndim
>> ind[axis] = np.newaxis
>
> Ouch! That doesn't handle axis=None.
>
> if axis:
> ind = [slice(None)] * x.ndim
> ind[axis] = np.newaxis
that's why I used
if axis != 0 and not axis is None:
and included a testcase for None. (although my version looks a bit
verbose but explicit)
Josef
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