[Numpy-discussion] sum returns grand total?

Travis Oliphant oliphant at ee.byu.edu
Mon Sep 11 10:47:18 CDT 2006


listservs at mac.com wrote:

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>I must have missed something -- since when does summing a  
>multidimensional array return the grand total? I thought that it  
>should sum over axis zero by default (at least, thats what the docs  
>say). Here's what I am getting:
>
>(Pdb) pre
>Out[6]:
>array([[[ 13,   3,   1,  33,  52],
>         [  1,   0,   0,   0,   2],
>         [  4,   0,   0,   2,   6],
>         [ 15,   1,   0,  20,  54]],
>
>        [[380, 101,   9, 267, 321],
>         [ 20,   4,   0,   7,  16],
>         [ 31,   3,   1,  31,  22],
>         [314,  27,   4, 276, 391]]], dtype=int64)
>(Pdb) sum(pre)
>Out[6]: 2432L
>
>Is this correct behaviour?
>  
>

Yes,  you need to specify which axis you want to sum over if you have a 
multi-dimensional array.  This is the "basic" behavior of most functions 
in numpy unless you import them from oldnumeric.   See the 
fix_default_axis.py file for help on converting code that worked for 
numpy 0.9.8 to 1.0 where this switch was made. 

-Travis





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