Q:

Finding items in one array based upon a second array

I have two arrays A and B:
A=array([[ 5.,   5.,   5.], 
         [ 8.,   9.,   9.]]) 
B=array([[ 1.,   1.,   2.], 
         [ 3.,   2.,   1.]]) 

Anywhere there is a "1" in B I want to sum the same row and column locations in A.
So for example for this one the answer would be 5+5+9=10
I would want this to continue for 2,3....n (all unique values in B)
So for the 2's... it would be 9+5=14 and for the 3's it would be 8
I found the unique values by using:
numpy.unique(B)

I realize this make take multiple steps but I can't really wrap my head around using the index matrix to sum those locations in another matrix. 

A:

For each unique value x, you can do
A[B == x].sum()

Example:
>>> A[B == 1.0].sum()
19.0

