title: Numpy remove duplicate column values
body: <p>I have a numpy array as follows</p>
  
  <pre><code>array([[ 6,  5],
     [ 6,  9],
     [ 7,  5],
     [ 7,  9],
     [ 8, 10],
     [ 9, 10],
     [ 9, 11],
     [10, 10]])
  </code></pre>
  
  <p>I want to pick elements such that y coordinates are unique. If two y coordinates are same I want to pick element with lesser x coordinate.</p>
  
  <p>Expected output</p>
  
  <pre><code>array([[ 6,  5],
     [ 6,  9],
     [ 8, 10],
     [ 9, 11]])
  </code></pre>
  
  <p>Explanation</p>
  
  <p>pick <code>[6,5]</code> over <code>[7,5]</code></p>
  
  <p>pick <code>[8,10]</code> over <code>[9,10]</code> and <code>[10,10]</code></p>
  
  <p>pick <code>[9, 11]</code></p>
  
  <p>Thanks</p>