title: Pandas series – lowest value in last x rows
body: <p>I am trying to build function that prints lowest value in last 10 rows into new column of my Pandas Dataframe hData.market_data["AAPL"]:</p>
  
  <pre><code>    close   volume  open    high    low
  2015-11-11  116.110001  45218000    116.370003  117.419998  115.209999
  2015-11-12  115.720001  32262600    116.260002  116.820000  115.650002
  2015-11-13  112.339996  45164100    115.199997  115.570000  112.269997
  2015-11-16  114.180000  37651000    111.379997  114.239998  111.000000
  2015-11-17  113.690002  27254000    114.919998  115.050003  113.320000
  2015-11-18  117.290001  46163400    115.760002  117.489998  115.500000
  2015-11-19  118.779999  42908200    117.639999  119.750000  116.760002
  2015-11-20  119.300003  34103500    119.199997  119.919998  118.849998
  2015-11-23  117.750000  32266700    119.269997  119.730003  117.339996
  2015-11-24  118.879997  42426900    117.330002  119.349998  117.120003
  </code></pre>
  
  <p>I came with this:</p>
  
  <pre><code>lowestlow = hData.market_data["AAPL"].low[-10:].min()
  hData.market_data["AAPL"]["Lowestlow10"] = lowestlow
  </code></pre>
  
  <p>but it prints the same minimum calculated from last 10 rows of the whole series (instead of the lowest low of last 10 rows that is calculated through the 
  series).
  Can you please advise me how to do it properly?</p>