title: How to merge all columns in a DataFrame except the first into one column and drop empty rows? Python
body: <p>I have a large dataframe with multiple columns, and want to merge all values  from all columns except the first one into one new column (<code>'New'</code>). Then drop rows for which <code>'New'</code> is empty. </p>
  
  <p>The <code>DataFrame</code> looks something like this (row <code>'C'</code> is empty):</p>
  
  <pre><code>    'Column1'  'Column2'  'Column3'  'Column4'  'Column5'  ...
  0    A          a
  1    B                     b
  2    C
  3    D          d
  4    E                                e
  5    F                                           f
  6    G                     g
  7    H                                h
  ...
  </code></pre>
  
  <p>The result I am looking for is this:</p>
  
  <pre><code>    'Column1'  'New'
  0    A          a
  1    B          b
  2    D          d
  3    E          e
  4    F          f
  5    G          g
  6    H          h
  ...
  </code></pre>
  
  <p>So the first column remains as it is and all other columns are merged into the column <code>'New'</code>. Since row <code>C</code> contains no value, it is dropped from the final <code>DataFrame</code>.</p>
  
  <p>What would be the most efficient way to achieve this?</p>