For example, given an array
arr = np.array([1,2,3,2,3,7,2,3,4])
there are 9 elements.
I want to get sum every 3 elements:
[6, 12, 9]
Is there any numpy api I can use?
sum every N elements from numpy array
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2 Answers
If your arr can be divided into groups of 3, i.e. has length 3*k, then:
arr.reshape(-1,3).sum(axis=-1)
# array([ 6, 12, 9])
In the general case, bincounts:
np.bincount(np.arange(len(arr))//3, arr)
# array([ 6., 12., 9.])
If the length of arr is not a multiple of 3, consider using np.add.reduceat:
>>> arr = np.array([1,2,3,2,3,7,2,3,4,5])
>>> np.add.reduceat(arr, np.arange(0, arr.size, 3))
array([ 6, 12, 9, 5])
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