title: How to replace one column with another using data.table?
body: <p>I have a dataframe:</p>
  <pre><code>ID      value1   value2
  1        f        a
  2        k        p
  3        c        j
  </code></pre>
  <p>I want to replace values in column value1 with values from value2 and remove column value2. So desired result is:</p>
  <pre><code>ID      value1   
  1        a        
  2        p        
  3        j        
  </code></pre>
  <p>I need to do it with data.table. And i need to do it with function, not recreating dataframe from scratch.</p>