[Numpy-discussion] Counting array elements

Tim Hochberg tim.hochberg at cox.net
Mon Oct 25 09:32:01 CDT 2004


Stephen Walton wrote:

>On Mon, 2004-10-25 at 10:26 +0200, Peter Verveer wrote:
>  
>
>>On 25 Oct 2004, at 04:17, Stephen Walton wrote:
>>    
>>
>>>I don't think we need sumall.  The methods and the functions should
>>>simply work the same way.  If one wants sumall, use A.flat.sum() or, if
>>>you can't use the methods or attributes on your old version of Python,
>>>sum(ravel(A)).
>>>      
>>>
>>I think this may be inefficient, because ravel and flat may make a copy 
>>of the data. Also I think using flat/ravel in such a way is plain ugly 
>>and a complex way to do it.
>>    
>>
>
>You may be right about the copying, I couldn't say.  I don't think
>sum(ravel(A)) looks any worse than sum(sum(sum(A))) for a rank 3 array,
>but ugly is in the eye of the beholder.
>  
>
I'm not sure how feasible it is, but I'd much rather an efficient, 
non-copying, 1-D view of an noncontiguous array (from an enhanced 
version of flat or ravel or whatever) than a bunch of extra methods. The 
former allows all of the standard methods to just work efficiently using 
sum(ravel(A)) or sum(A.flat) [ and max and min, etc]. Making special 
whole array methods for everything just leads to method eplosion.

-tim



>  
>
>>In my opinion functions that calculate a statistic like sum 
>>should return the total in the first place, rather then over a single 
>>axis.
>>    
>>
>
>It depends on the data.  I use rank-2 arrays which are images and are
>therefore homogeneous.  Even there, though, I often want the sum of all
>rows or all columns.  For heterogeneous data (e.g., columns of different
>Y's as a function of X), the present sum() makes sense.  In other words,
>we will always need ways to sum over just one dimension and over all
>dimensions.  By analogy with MATLAB (I'm guessing), sum() in Numeric and
>numarray does a one-D sum.
>
>  
>






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