title: How do you use "<<-" (scoping assignment) in R?
body: <p>I just finished reading about <a href="http://cran.r-project.org/doc/manuals/R-intro.html#Scope" rel="noreferrer">scoping in the R intro</a>, and am very curious about the <code>&lt;&lt;-</code> assignment.</p>
  
  <p>The manual showed one (very interesting) example for <code>&lt;&lt;-</code>, which I feel I understood. What I am still missing is the context of when this can be useful.</p>
  
  <p>So what I would love to read from you are examples (or links to examples) on when the use of <code>&lt;&lt;-</code> can be interesting/useful.  What might be the dangers of using it (it looks easy to loose track of), and any tips you might feel like sharing.</p>