Question

I’m translating some stuff from MATLAB to the Python language.

There’s this command, unique(a), in NumPy. But since the MATLAB program runs the ‘rows’ command also, it gives something a little different.

Is there a similar command in Python or should I make some algorithm that does the same thing?

Answer 1

Assuming your 2D array is stored in the usual C order (that is, each row is counted as an array or list within the main array; in other words, row-major order), or that you transpose the array beforehand otherwise, you could do something like…

>>> import numpy as np
>>> a = np.array([[1, 2, 3], [2, 3, 4], [1, 2, 3], [3, 4, 5]])
>>> a
array([[1, 2, 3],
       [2, 3, 4],
       [1, 2, 3],
       [3, 4, 5]])
>>> np.array([np.array(x) for x in set(tuple(x) for x in a)]) # or "list(x) for x in set[...]"
array([[3, 4, 5],
       [2, 3, 4],
       [1, 2, 3]])

Of course, this doesn’t really work if you need the unique rows in their original order.

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By the way, to emulate something like unique(a, 'columns'), you’d just transpose the original array, do the step shown above, and then transpose back.