title: For each row return the column name of the largest value
body: <p>I have a roster of employees, and I need to know at what department they are in most often. It is trivial to tabulate employee ID against department name, but it is trickier to return the department name, rather than the number of roster counts, from the frequency table. A simple example below (column names = departments, row names = employee ids).</p>
  
  <pre><code>DF &lt;- matrix(sample(1:9,9),ncol=3,nrow=3)
  DF &lt;- as.data.frame.matrix(DF)
  &gt; DF
    V1 V2 V3
  1  2  7  9
  2  8  3  6
  3  1  5  4
  </code></pre>
  
  <p>Now how do I get</p>
  
  <pre><code>&gt; DF2
    RE
  1 V3
  2 V1
  3 V2
  </code></pre>