Build sum of array based on index array [duplicate]

I have three arrays

A = array([0, 0, 0, 0])

B = array([0.4, 0.3, 0.2, 0.1])

C = array([0, 0, 1, 2])

I want to assign to every element i of array A the sum of all elements of array B for which array C points to i. The result should be

A = array([0.7, 0.2, 0.1, 0])

So far I get the desired result as follows:

for i in np.unique(C):
 A[i] = np.sum(B[C==i])

The arrays are large, and the loop is slow. I am trying to accomplish this without a loop, but I don't know how. Thank you for suggestions!