code: def arr_union(ar1, ar2):
      if ar1.shape[0] == 0:
          return ar2
      elif ar2.shape[0] == 0:
          return ar1
      else:
          return arr_unique(np.concatenate((ar1, ar2)))
  
imports: from __future__ import print_function
  import locale
  import numpy
  import numba
  from pynndescent.utils import norm, tau_rand
  from pynndescent.distances import kantorovich, jensen_shannon_divergence, symmetric_kl_divergence
label_desc: Use image node_id 3 for calling a global function with example usage: arr_union(ar1, ar2) and returns: ar2, ar1, arr_unique