[Numpy-discussion] using reducing functions without eliminating dimensions?
Thu Apr 9 01:29:49 CDT 2009
2009/4/9 Charles R Harris <firstname.lastname@example.org>:
> On Tue, Apr 7, 2009 at 12:44 PM, Dan Lenski <email@example.com> wrote:
>> Hi all,
>> I often want to use some kind of dimension-reducing function (like min(),
>> max(), sum(), mean()) on an array without actually removing the last
>> dimension, so that I can then do operations broadcasting the reduced
>> array back to the size of the full array. Full example:
>> >> table.shape
>> (47, 1814)
>> >> table.min(axis=1).shape
>> >> table - table.min(axis=1)
>> ValueError: shape mismatch: objects cannot be broadcast to a single
>> >> table - table.min(axis=1)[:, newaxis]
>> I have to resort to ugly code with lots of stuff like "... axis=1)[:,
>> Is there any way to get the reducing functions to leave a size-1 dummy
>> dimension in place, to make this easier?
> Not at the moment. There was talk a while back of adding a keyword for this
> option, it would certainly make things easier for some common uses. It might
> be worth starting that conversation up again.
What's wrong with np.amin(a,axis=-1)[...,np.newaxis]?
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