Sorting a 2D numpy array by multiple axes

Question

I have a 2D numpy array of shape (N,2) which is holding N points (x and y coordinates). For example:

array([[3, 2],
       [6, 2],
       [3, 6],
       [3,          


        

Answer 1

You can use np.complex_sort. This has the side effect of changing your data to floating point, I hope that's not a problem:

>>> a = np.array([[3, 2], [6, 2], [3, 6], [3, 4], [5, 3]])
>>> atmp = np.sort_complex(a[:,0] + a[:,1]*1j)
>>> b = np.array([[np.real(x), np.imag(x)] for x in atmp])
>>> b
array([[ 3.,  2.],
       [ 3.,  4.],
       [ 3.,  6.],
       [ 5.,  3.],
       [ 6.,  2.]])