title: sort pandas dataframe by sum of columns
body: <p>I have a dataframe that looks like this</p>
  
  <pre><code>            Australia  Austria    United Kingdom  Vietnam
  date                                                    
  2020-01-30          9        0                 1       2
  2020-01-31          9        9                 4       2
  </code></pre>
  
  <p>I would like to crate a new dataframe that inclues countries that have sum of their column > 4 and I do it</p>
  
  <pre><code>df1 = df[[i for i in df.columns if int(df[i].sum()) &gt; 4]]
  </code></pre>
  
  <p>this gives me </p>
  
  <pre><code>            Australia  Austria    United Kingdom  
  date                                                     
  2020-01-30          9        0                 1      
  2020-01-31          9        9                 4 
  </code></pre>
  
  <p>I now would like to sort the countries based on the sum of their column and than take the first 2</p>
  
  <pre><code>            Australia  Austria   
  date                                    
  2020-01-30          9        0        
  2020-01-31          9        9
  </code></pre>
  
  <p>I know I have to use <em>sort_values</em> and <em>tail</em>. 
  I just can't workout how</p>