title: Merge multiple column values into one column in python pandas
body: <p>I have a pandas data frame like this:</p>
  
  <pre><code>   Column1  Column2  Column3  Column4  Column5
   0    a        1        2        3        4
   1    a        3        4        5
   2    b        6        7        8
   3    c        7        7        
  </code></pre>
  
  <p>What I want to do now is getting a new dataframe containing Column1 and a new columnA. This columnA should contain all values from columns 2 -(to) n (where n is the number of columns from Column2 to the end of the row) like this:</p>
  
  <pre><code>  Column1  ColumnA
  0   a      1,2,3,4
  1   a      3,4,5
  2   b      6,7,8
  3   c      7,7
  </code></pre>
  
  <p>How could I best approach this issue? Any advice would be helpful. Thanks in advance!</p>