title: Max and Min value for each colum of one Dataframe
body: <p>Give this dataframe 'x':</p>
  
  <pre><code>    col1 col2 col3 col4
      0     5   -2    1 
     -5     2   -1    9
      3    -7    3    5
  </code></pre>
  
  <p>How I could get a list of pairs with the min and max of each column? The result would be:</p>
  
  <pre><code>list = [ [-5 , 3], [-7 , 5], [-2 , 3], [1 , 9] ]
  </code></pre>