title: R match/%in% for data frames
body: <p>I'm trying to find those rows in a data frame, which appear in another data frame.</p>
  
  <pre><code>df1 &lt;- data.frame(V1=c(0,1,1,1), V2=c(0,1,0,2))
  df2 &lt;- data.frame(V1=c(0,1), V2=c(0,1))
  
  in_df(df1, df2) # should yield c(T, T, F, F)
  </code></pre>
  
  <p>Is there a function which calculates this?</p>