[Numpy-discussion] summing over more than one axis

greg whittier gregwh@gmail....
Thu Aug 19 09:01:02 CDT 2010

I frequently deal with 3D data and would like to sum (or find the
mean, etc.) over the last two axes.  I.e. sum a[i,j,k] over j and k.
I find using .sum() really convenient for 2d arrays but end up
reshaping 2d arrays to do this.  I know there has to be a more
convenient way.  Here's what I'm doing

a = np.arange(27).reshape(3,3,3)

# sum over axis 1 and 2
result = a.reshape((a.shape[0], a.shape[1]*a.shape[2])).sum(axis=1)

Is there a cleaner way to do this?  I'm sure I'm missing something obvious.


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