title: Pandas Data Frame saving into csv file
body: <p>I wonder how to save a new pandas Series into a csv file in a different column. Suppose I have two csv files which both contains a column as a 'A'. I have done some mathematical function on them and then create a new variable as a 'B'.</p>
  
  <p>For example: </p>
  
  <pre><code>data = pd.read_csv('filepath')
  
  data['B'] = data['A']*10
  
  # and add the value of data.B into a list as a B_list.append(data.B) 
  </code></pre>
  
  <p>This will continue until all of the rows of the first and second csv file has been reading. </p>
  
  <p>I would like to save a column B in a new spread sheet from both csv files.
  For example I need this result:</p>
  
  <pre><code>colum1(from csv1)        colum2(from csv2)     
       data.B.value             data.b.value
  </code></pre>
  
  <p>By using this code:</p>
  
  <pre><code>pd.DataFrame(np.array(B_list)).T.to_csv('file.csv', index=False, header=None)
  </code></pre>
  
  <p>I won't get my preferred result. </p>