title: Double merge two data frames in r
body: <p>I have two dataframes</p>
  
  <pre><code>df1 = data.frame(Sites=c("A","B","C"),total=c(12,6,35))
  
  df2 = data.frame(Site.1=c("A","A","B"),Site.2=c("B","C","C"), Score=c(60,70,80))
  </code></pre>
  
  <p>I need to merge them to produce the dataframe</p>
  
  <pre><code>df3=data.frame(Site.1=c("A","A","B"),Site.2=c("B","C","C"),
  Score=c(60,70,80),Site.1.total=c(12,12,6),Site.2.total=c(6,35,35))
  </code></pre>
  
  <p>Any advice on the simplest way to do such a double merge? Thanks</p>