title: pandas, split, or divide(subtract) dataframe
body: <p>I have a dataframe "moment_f". 
  and i have to delete some rows from moment_f that contains the name "AH".
  However I shall not delete every "AH" rows so I made a new dataframe that
  contains the "AH" that I want to delete. </p>
  
  <pre><code>ah1 = moment_f[moment_f["TextGridLabel"] == "AH"]
  ah_d = ah1.iloc[::2] 
  # got the odd rows of "AH" which is what I need to get rid of from the original dataframe "moment_f". 
  </code></pre>
  
  <p>so now I want to delete dataframe"ah_d" from dataframe "moment_f". </p>
  
  <p>What would be the opposite of concatenation? 
  I've tried drop, split, etc but it doesn't work. </p>