title: Remove common elements in numpy array
body: <p>I am trying to do a union of two numpy arrays in the following manner</p>
  
  <pre><code>np.union1d( np.arange(0.1, 0.91, 0.1), np.arange(0.4, 0.81, 0.01)  )
  </code></pre>
  
  <p>The output reads:</p>
  
  <pre><code>array([ 0.1 ,  0.2 ,  0.3 ,  0.4 ,  0.41,  0.42,  0.43,  0.44,  0.45,
      0.46,  0.47,  0.48,  0.49,  0.5 ,  0.5 ,  0.51,  0.52,  0.53,
      0.54,  0.55,  0.56,  0.57,  0.58,  0.59,  0.6 ,  0.6 ,  0.61,
      0.62,  0.63,  0.64,  0.65,  0.66,  0.67,  0.68,  0.69,  0.7 ,
      0.7 ,  0.71,  0.72,  0.73,  0.74,  0.75,  0.76,  0.77,  0.78,
      0.79,  0.8 ,  0.8 ,  0.9 ])
  </code></pre>
  
  <p>In the output of this union, the number 0.5 features twice. Even when I use the unique function in numpy, this replication of the number 0.5 doesn't go away. Meaning:</p>
  
  <pre><code>np.unique( np.union1d( np.arange(0.1, 0.91, 0.1), np.arange(0.4, 0.81, 0.01)  ) )
  </code></pre>
  
  <p>also gives the same output. What am I doing wrong? How can I correct this and get the desired output (i.e. have only one occurrence of the number 0.5 in my array? </p>