title: Concatenate string to data frame column
body: <p>I want to append to a data.frame the same string.</p>
  
  <pre><code>&gt; df1 &lt;- data.frame(pt1="a", pt2="b", row.names=1)
  &gt; df1
    pt1 pt2
  1   a   b
  </code></pre>
  
  <p>As a result I would like to have:</p>
  
  <pre><code>   pt1                 pt2
  1  Add this string a   Add this string b
  </code></pre>