title: Column extract a variable from data frame
body: <p>simple question ahoy:</p>
  
  <p>I have a data frame with three columns: a,b,c. How would I extract a specific column from a variable? For example:</p>
  
  <pre><code>test &lt;- data.frame(3,4,5)
  column = "X4"
  </code></pre>
  
  <p>If I try</p>
  
  <pre><code>test$column
  </code></pre>
  
  <p>I get <code>NULL</code>. If I try</p>
  
  <pre><code>test$X4
  </code></pre>
  
  <p>I get the right answer of <code>4</code>. What am I missing about the test$column bit that isn't working the way I want it to? Thanks!</p>