title: DataFrame.drop_duplicates and DataFrame.drop not removing rows
body: <p>I have read in a csv into a pandas dataframe and it has five columns. Certain rows have duplicate values only in the second column, i want to remove these rows from the dataframe but neither drop nor drop_duplicates is working.</p>
  
  <p>Here is my implementation:</p>
  
  <pre><code>#Read CSV
  df = pd.read_csv(data_path, header=0, names=['a', 'b', 'c', 'd', 'e'])
  
  print Series(df.b)
  
  dropRows = []
  #Sanitize the data to get rid of duplicates
  for indx, val in enumerate(df.b): #for all the values
      if(indx == 0): #skip first indx
          continue
  
      if (val == df.b[indx-1]): #this is duplicate rtc value
          dropRows.append(indx)
  
  print dropRows
  
  df.drop(dropRows) #this doesnt work
  df.drop_duplicates('b') #this doesnt work either
  
  print Series(df.b)
  </code></pre>
  
  <p>when i print out the series df.b before and after they are the same length and I can visibly see the duplicates still. is there something wrong in my implementation?</p>