title: How to map values from a data.table to a data.table (R)
body: <p>I have two map/data.tables. One consists of key-values and another one just of some keys. I want to map the values from the first map to the keys of the second. How can this be done?</p>
  
  <p>Here is some example code:</p>
  
  <pre><code>map1&lt;-data.table( k=c("A","B"), v=c(2,3) )
  map2&lt;-data.table( k2=c("A","B","A","A"))
  </code></pre>
  
  <p>How can I produce a new column v2 in map2 which contains c(2,3,2,2)?</p>