I want to add the values of a vector:
a = np.array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9], dtype='d')
to the values of another vector:
c = np.array([10, 10, 10], dtype='d')
at position given by another array (of the same size of a, with values 0 <= b[i] < len(c))
b = np.array([2, 0, 1, 0, 2, 0, 1, 1, 0, 2], dtype='int32')
This is very simple to write in pseudo code:
for I in range(b.shape[0]):
J = b[I]
c[J] += a[I]
Something like this, but vectorized (length of c is some hundreds in real case).
c[0] += np.sum(a[b==0]) # 27 (10 + 1 + 3 + 5 + 8)
c[1] += np.sum(a[b==1]) # 25 (10 + 2 + 6 + 7)
c[2] += np.sum(a[b==2]) # 23 (10 + 0 + 4 + 9)
My initial guess was:
c[b] += a
but only last values of a are summed.
