title: Return a pandas series of date time in chronological order by the original series' indices
body: <p>I compiled a pandas series of date time like the following (the below shows part of the series as an example):</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
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  <pre class="snippet-code-css lang-css prettyprint-override"><code>0   2002-02-03
  1   1979-01-01
  2   2006-12-25
  3   2008-07-16
  4   2005-05-30</code></pre>
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  <p>Note: the dtype of each cell is 'pandas._libs.tslib.Timestamp'</p>
  
  <p>For the above example, I would like to rank them by chronological order and return a series by the original series' indices like this (the second column):</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
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  <pre class="snippet-code-css lang-css prettyprint-override"><code>0   1
  1   0
  2   3
  3   4
  4   2</code></pre>
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  <p>I've tried using a mix of .order(), .sort(), and .index() to achieve this but to no avail so far. What will be the easiest way to do get a series of date time in chronological order by the original series' indices?</p>
  
  <p>Thank you.</p>