title: Getting smallest value of a column in last n rows
body: <p>The title of this might be a bit confusing but i will try to explain what i am trying to do. I have an OHLC csv of stocks. I am trying to add a new column named L and H. Here what represents. I need to check for the smallest Open price in last n days (say 5). and i need to set it's Low price to L and High price as H.</p>
  
  <p>Here is my Dataframe</p>
  
  <pre><code>            Date     Open     High      Low
  5303  2018-06-11  1681.51  1694.24  1680.59
  5304  2018-06-12  1693.00  1699.51  1691.52
  5305  2018-06-13  1702.81  1713.75  1700.12
  5306  2018-06-14  1713.48  1724.80  1708.87
  5307  2018-06-15  1714.00  1720.87  1708.52
  5308  2018-06-18  1706.26  1726.74  1702.56
  5309  2018-06-19  1709.04  1736.11  1700.39
  5310  2018-06-20  1742.50  1762.93  1741.36
  5311  2018-06-21  1760.00  1763.10  1717.56
  5312  2018-06-22  1742.62  1743.00  1711.90
  </code></pre>
  
  <p>I have tried the following way but it only returns the minimum value not the Series i can grab High and Low</p>
  
  <pre><code>df['Open'].rolling(5).min()
  </code></pre>
  
  <p>Here i am trying to get the index or whole Dataframe series of <code>rolling()</code> to grab Hig and Low values of this rolling. I hope I could explain.</p>
  
  <p>EDIT: Added expected output</p>
  
  <p>Let's say index 5308 is the smallest Open in last 5 rows. So L will be equal to 5308's <code>Low</code> column and H will be equal to 5308's <code>High</code> column in the rest of data</p>
  
  <pre><code>            Date     Open     High      Low        H        L
  5309  2018-06-19  1709.04  1736.11  1700.39  1726.74  1702.56
  5310  2018-06-20  1742.50  1762.93  1741.36  1726.74  1702.56
  5311  2018-06-21  1760.00  1763.10  1717.56  1726.74  1702.56
  5312  2018-06-22  1742.62  1743.00  1711.90  1726.74  1702.56
  </code></pre>