CODEWITHSUNDEEP
pythonarraysnumpynumpy-ndarray
noob
noob

Reputation: 6854

Numpy.sum() nD array of (2,2,2...n) to a 1D array of shape (2,)

I want to numpy.sum() my nD arrays (matrix) of shape (2,2,2...n) to 1D arrays of shape (2,).

Basically along the axis=0. (Sum the first number of each 1d array of shape (2,) and sum the second number of the same arrays into one single resulting 1d array of shape (2,)).

However matrix.sum(axis=0) only seems to work for those of shape (2,2), while I think matrix.sum(axis=(1,2)) works for (2,2,2). But then what about (2,2,2,2) arrays and so on?

The n-dimensions have been confusing me. A generalised solution, along with a brief explanation, would be much appreciated.

EDIT: I've provided an example of the nD arrays I'm trying to sum below. I want to sum along axis=0 to get a (2,) 1D array. numpy.sum(axis=0) seems to only work for the array of shape (2,2)... 

#Of shape (2,2):
[[9.99695358e-02 9.99232016e-01]
 [9.00030464e-01 7.67983971e-04]].sum(axis=0) seems to work

#Of shape (2,2,2):
[[[2.02737071e-01 7.75883149e-01]
  [2.02650032e-08 1.58192237e-02]]
 [[7.31718878e-06 1.41793363e-03]
  [4.12802168e-03 7.26350831e-06]]].sum(axis=(1,2)) seems to work

#Of shape… (2,2,2,2)
[[[[1.83819962e+00 1.02712560e-02]
   [5.05122135e-02 2.80555725e-04]]
  [[5.60304309e-07 5.44521143e-04]
   [2.41592380e-03 1.49436734e-05]]]
 [[[7.04398015e-05 7.66717944e-06]
   [1.76843337e-05 1.98868986e-06]]
  [[9.74010599e-02 1.12527543e-07]
   [2.61427056e-04 2.70778171e-08]]]].sum(axis=?) # What axis? And how to generalise?

Upvotes: 1

Views: 149

Answers (1)

tstanisl
tstanisl

Reputation: 14107

What do you think about reshaping x to 2D and summing along the second axis?

x.reshape(x.shape[0], -1).sum(axis=1)

Upvotes: 1

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