Numpy sum of values in subarrays between pairs of indices

Question

Suppose I have an array A. I have a series of index pairs (a1, b1), (a2, b2) ... (an, bn)

I want to obtain all the sums of the elements between those pairs. i.e.

Answer 1

Assuming your index pairs are stored in a NumPy array indices of shape (n, 2) and n is fairly large, it is probably best to avoid any Python loop:

c = numpy.r_[0, A.cumsum()][indices]
sums = c[:,1] - c[:,0]