title: Why is an extra character ("X") added to the rownames of my data.frame?
body: <p>Originally the <code>rownames</code> of my data (a <code>csv</code>-file) were:</p>
  
  <pre><code>1
  5
  33
  37
  </code></pre>
  
  <p>However, as I read in my data using:</p>
  
  <pre><code>data &lt;- read.table(data, sep = ",", header = TRUE)
  </code></pre>
  
  <p>it seems that the <code>rownames</code> has been transformed to: </p>
  
  <pre><code>X1
  X5
  X33
  X37
  </code></pre>
  
  <p>Are there any common reasons for why this is happening? It's entirely unintentional.</p>