title: How do I paste string columns in data.frame
body: <p>suppose we have: </p>
  
  <pre><code>mydf &lt;- data.frame(a= LETTERS, b = LETTERS, c =LETTERS)
  </code></pre>
  
  <p>Now we want to add a new column, containing a concatenation of all columns. 
  So that rows in the new column read "AAA", "BBB", ...</p>
  
  <p>In my mind the following should work?  </p>
  
  <pre><code>mydf[,"Concat"] &lt;- apply(mydf, 1, paste0)
  </code></pre>