title: by command to find out the maximum number from a list
body: <p>I have a list like this :</p>
  
  <pre><code>Ll 
  $a
  3.4 5.6 -2.1 -7.8
  $b
  2.1 6.7
  $c
  -6.7,0.001,8.9
  </code></pre>
  
  <p>I want to find out the maximum number for all elements of the list irrespective of the signs.
  i.e. I want my out put to look like this : </p>
  
  <pre><code>Ll
  $a
  -7.8
  $b
  6.7
  $c
  8.9
  </code></pre>
  
  <p>Is there a way to do this through single command line ?
  Can it be done using the 'by' command?</p>