title: Why doesn't R allow $ operator on atomic vectors?
body: <p>The following will throw the error "Error in v$a : $ operator is invalid for atomic vectors" (at least in R version 2.14.1):</p>
  
  <pre><code>v &lt;- c(a='a',b='b')
  v$a
  </code></pre>
  
  <p>Apparently, R previously allowed this, which makes me curious as to why.</p>
  
  <p>EDIT: As pointed out below, <code>v$a</code> would have returned NULL in the earlier versions. Changed "fairly recently" to "previously", since I based this on old Internet forums and have been corrected below.</p>