title: Selecting pandas column by location
body: <p>I'm simply trying to access named pandas columns by an integer. </p>
  
  <p>You can select a row by location using <code>df.ix[3]</code>.</p>
  
  <p>But how to select a column by integer?</p>
  
  <p>My dataframe:</p>
  
  <pre><code>df=pandas.DataFrame({'a':np.random.rand(5), 'b':np.random.rand(5)})
  </code></pre>