title: Python Pandas Select Index where index is larger than x
body: <p>Say I have a DataFrame <code>df</code> with date as index and some values. How can I select the rows where the date is larger than some value <code>x</code>? </p>
  
  <p>I know I can convert the index to a column and then do the select <code>df[df['date']&gt;x]</code>, but is that slower than doing the operation on the index?</p>