title: Torch/Lua equivalent function to MATLAB or Numpy 'Unique'
body: <p>In Python one can do the following to get the unique values in a vector/matrix/tensor:</p>
  
  <pre><code>import numpy as np
  
  a = np.unique([1, 1, 2, 2, 3, 3])
  # Now a = array([1, 2, 3])
  </code></pre>
  
  <p>There is a similar function in MATLAB as well:</p>
  
  <pre><code>A = [9 2 9 5];
  C = unique(A)
  %Now C = [9, 2, 9]
  </code></pre>
  
  <p>Is there an equivalent function in Torch/Lua as well?</p>