title: Pandas: select rows where two columns are different
body: <p>Suppose I have a dataframe as below</p>
  
  <pre><code>a  b  c  
  1  1  45
  0  2  74
  2  2  54
  1  4  44
  </code></pre>
  
  <p>Now I want the rows where column a and b are not same. So the expected outpu is</p>
  
  <pre><code>a  b  c 
  0  2  74
  1  4  44
  </code></pre>
  
  <p>How can I do this?</p>