Find indexes of matching rows in two 2-D arrays

Question

Suppose that I have two 2-D arrays as follows:

array([[3, 3, 1, 0],
       [2, 3, 1, 3],
       [0, 2, 3, 1],
       [1, 0, 2, 3],
       [3, 1, 0, 2]], dtype=in         


        

Answer 1

I can't think of a numpy specific way to do it, but here's what I would do with regular lists:

>>> L1= [[3, 3, 1, 0],
...        [2, 3, 1, 3],
...        [0, 2, 3, 1],
...        [1, 0, 2, 3],
...        [3, 1, 0, 2]]
>>> L2 = [[0, 3, 3, 1],
...        [0, 2, 3, 1],
...        [1, 0, 2, 3],
...        [3, 1, 0, 2],
...        [3, 3, 1, 0]]
>>> L1 = {tuple(row):i for i,row in enumerate(L1)}
>>> answer = []
>>> for i,row in enumerate(L2):
...   if tuple(row) in L1:
...     answer.append((L1[tuple(row)], i))
... 
>>> answer
[(2, 1), (3, 2), (4, 3), (0, 4)]