title: Adding values to all rows of dataframe
body: <p>I have two pandas dataframes <strong><em>df1</em></strong> (of length 2) and <strong><em>df2</em></strong> (of length about 30 rows). Index values of df1 are always different and never occur in df2. I would like to add the average of columns from <strong><em>df1</em></strong>  to corresponding columns of <strong><em>df2</em></strong>. Example: add 0.6 to all rows of c1 and 0.9 to all rows of c2 etc ...</p>
  
  <pre><code>df1: 
    Date       c1   c2   c3   c4    c5   c6 ...  c10
  2017-09-10  0.5  0.6  1.2   0.7  1.3  1.8 ...  1.3
  2017-09-11  0.7  1.2  1.3   0.4  0.7  0.4 ...  1.5
  
  
  df2:
    Date       c1   c2   c3   c4    c5   c6 ...  c10
  2017-09-12  0.9  0.1  1.4   0.9  1.5  1.9 ...  1.9
  2017-09-13  0.2  1.8  1.2   1.4  2.7  0.8 ...  1.1
      :                                  :  
      :                                  :     
  2017-10-10  1.5  0.9  1.5   0.9  1.6  1.8 ...  1.7
  2017-10-11  2.7  1.1  1.9   0.4  0.8  0.8 ...  1.3
  </code></pre>
  
  <p>How can I do that ?</p>