title: Access to R Column not defined
body: <p>I have a very simple script:</p>
  <pre><code>u2 &lt;- 1:10
  usq2 &lt;- u2 * u2
  m2 &lt;- cbind(u2,usq2)
  df2 &lt;- as.data.frame(m2)
  </code></pre>
  <p>str(df2) shows two columns u2 and usq2</p>
  <p>How come I have access to df2$usq also? The output is the same as df2$usq2! I cleared my environment before executing this script.</p>