title: How to get the deltas of a list collection
body: <p>I have a list.</p>
  
  <blockquote>
    <p>1 2 3 4 5 6 7</p>
  </blockquote>
  
  <p>I wish to return a list of differences (deltas) between consecutive element.</p>
  
  <blockquote>
    <p>1 1 1 1 1 1</p>
  </blockquote>
  
  <p>How can I do this?</p>
  
  <p>I am sure there must be a simple "collections" way of doing this - but I cannot find it.</p>