title: how assign "NA" value into new column in python and pandas
body: <p>I am not able to assign NA values to dataframe and while exporting to_csv file,its shows empty. please suggest.</p>
  <p><a href="https://i.stack.imgur.com/lMO1F.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/lMO1F.png" alt="enter image description here" /></a></p>
  <p>Looking out put of Data_1 is :</p>
  <p><a href="https://i.stack.imgur.com/1hAml.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/1hAml.png" alt="enter image description here" /></a></p>
  <pre><code>for i in range(1, length):
      Nnw_ = np.array(data_1.iloc[0:(data_1.iloc[0:, i]).count(),[i]])
      rep = np.array(data_2.iloc[0:( data_2.iloc[0:, i]).count(),[i + 1]])
      data_1.replace(Nnw, rep, inplace=True)
  </code></pre>