title: Create flag column set from original columns, '1' when missing values
body: <p>Apologies if this is a simple issue, I am trying to tech myself python.  I have a panda dataframe that has a large number of columns with missing values. I am going to impute those values for the modeling part, but I also want to see if the fact that they are missing is important. </p>
  
  <p>To do this I am trying to create a second set of binary columns that are 1 when the observation in the column is null, 0 else.  My code is as follows:</p>
  
  <pre><code>test=train_17
  col_names=test.columns.tolist()
  for col in col_names:
      for row in test[col]:
          if test[col][row].isnull():
              test[col+"_missing"] = 1
          else:
              test[col+"_missing"] = 0
  </code></pre>
  
  <p>When I attempt to do this I get a kKeyError: 14297519. In the log I also see this:</p>
  
  <pre><code>tz=getattr(series.dtype, 'tz', None))
  </code></pre>
  
  <p>Does anybody have any thoughts or suggestions about what I am doing wrong?</p>