title: Specifying column names in a data.frame changes spaces to "."
body: <p>Let's say I have a data.frame, like so: </p>
  
  <pre><code>x &lt;- c(1:10,1:10,1:10,1:10,1:10,1:10,1:10,1:10,1:10,1:10)
  df &lt;- data.frame("Label 1"=x,"Label 2"=rnorm(100))
  </code></pre>
  
  <p>head(df,3)</p>
  
  <p>returns:</p>
  
  <pre><code>  Label.1    Label.2
  1       1  1.9825458
  2       2 -0.4515584
  3       3  0.6397516
  </code></pre>
  
  <p>How do I get R to stop automagically replacing the space with a period in the column name? ie, "Label 1" instead of "Label.1".</p>