title: Pandas drop function not working in a for loop?
body: <p>all!
  I am pretty confused by this and for the life of me cannot figure out the error.
  I am trying to go through all the strings in a data frame and remove the ones that do not contain the string 'Barry Bonds'.</p>
  
  <p>So far I have managed to be able to drop rows by their index:</p>
  
  <pre><code>bb_db.drop(bb_db.index[1])
  </code></pre>
  
  <p>This is successful at dropping the row at that index, however when I throw it into this for loop:</p>
  
  <pre><code>for i in range(len(bb_db)):
      if 'Barry Bonds' in bb_db['player_names'][i]:
          bb_db.drop(bb_db.index[i])
          print (i)
  </code></pre>
  
  <p>I get the entire dataframe, even though the i variable prints out a ton of indexes with the if statement as being true.</p>
  
  <p>Thank you!</p>