title: Filtering string/float/integer values in pandas dataframe columns
body: <p>How can I filter only string values/ integer/ float values in one column  (<code>SIC</code>) in a pandas data frame like below?</p>
  <pre><code>                         SIC
  1                      246804
  2                      135272
  3                      898.01
  4                     3453.33
  5                       shine  
  6                        add
  7                         522
  8                         Nan
  9                      string
  10                      29.11
  11                        20    
  </code></pre>