title: Main difference between map and reduce
body: <p>I used both methods but I am quite confused regarding the usage of both methods.</p>
  
  <p>Is anything that <code>map</code> can do but <code>reduce</code> can not and vice versa?</p>
  
  <p>Note: I know how to use both methods I am questioning for main difference between these method and when we need to used.</p>