check for identical rows in different numpy arrays

Question

how do I get a row-wise comparison between two arrays, in the result of a row-wise true/false array?

Given datas:

a = np.array([[1,0],[2,0],[3,1],[4,2]])
b = np.array([[1,0],[2,0],[4,2]])

Result step 1:

c = np.array([True, True,False,True])

Result final:

a = a[c]

So how do I get the array c ????

P.S.: In this example the arrays a and b are sorted, please give also information if in your solution it is important that the arrays are sorted

Answer 1

Here's a vectorised solution:

res = (a[:, None] == b).all(-1).any(-1)

print(res)

array([ True,  True, False,  True])

Note that a[:, None] == b compares each row of a with b element-wise. We then use all + any to deduce if there are any rows which are all True for each sub-array:

print(a[:, None] == b)

[[[ True  True]
  [False  True]
  [False False]]

 [[False  True]
  [ True  True]
  [False False]]

 [[False False]
  [False False]
  [False False]]

 [[False False]
  [False False]
  [ True  True]]]