Numpy: Row Wise Unique elements

Question

Does any one know how to get unique elements row wise in a matrix. For e.g. input matrix may be like:

a = [[1,2,1,3,4,1,3],
     [5,5,3,1,5,1,2],
     [1,2,3         


        

Answer 1

The fastest way should be to set all duplicates to zero using sort and diff:

def row_unique(a):
    unique = np.sort(a)
    duplicates = unique[:,  1:] == unique[:, :-1]
    unique[:, 1:][duplicates] = 0
    return unique

This is about 3 times as fast as the unutbu's solution on my computer:

In [26]: a = np.random.randint(1, 101, size=100000).reshape(1000, 100)

In [27]: %timeit row_unique(a)
100 loops, best of 3: 3.18 ms per loop

In [28]: %timeit using_complex(a)
100 loops, best of 3: 15.4 ms per loop

In [29]: assert np.all(np.sort(using_complex(a)) == np.sort(row_unique(a)))