title: Check for unique numbers and extract index
body: <p>I have a list of floats:</p>
  
  <pre><code>x = [1.69,1.69,2.36,2.63,2.63,3.00,3.00]
  </code></pre>
  
  <p>Finally I try to get a list with all equal numbers: </p>
  
  <pre><code>y = [1.69,1.69,2.63,2.63,3.00,3.00]
  </code></pre>
  
  <p>and the indices of unique numbers:</p>
  
  <pre><code> z = [2]
  </code></pre>