Cumulative summation of a numpy array by index

Question

Assume you have an array of values that will need to be summed together

d = [1,1,1,1,1]

and a second array specifying which elements need to be

Answer 1

def zeros(ilen):
 r = []
 for i in range(0,ilen):
     r.append(0)

i_list = [0,0,1,2,2]
d = [1,1,1,1,1]
result = zeros(max(i_list)+1)

for index in i_list:
  result[index]+=d[index]

print result