Sum slices of consecutive values in a NumPy array

Question

Let\'s say I have a numpy array a containing 10 values. Just an example situation here, although I would like to repeat the same for an array with length 100.

Answer 1

Here's (yet) another solution:

In [3]: a.reshape((2,5)).sum(axis=1)
Out[3]: array([15, 40])

Reshape the one-dimensional array to two rows of 5 columns and sum over the columns:

In [4]: a.reshape((2,5))
Out[4]: 
array([[ 1,  2,  3,  4,  5],
       [ 6,  7,  8,  9, 10]])

The sum along each row (summing the column entries) is specified with axis=1. The reshape happens without copying data (and without modifying the original a) so it is efficient and fast.