title: replace value in dataframe based on another data frame
body: <p>I have the following two dataframes:</p>
  
  <pre><code>&gt;df1&lt;-data.frame(A=c(0,0,0),B=c(0,201,0),C=c(0,467,0))
    A   B   C
  1 0   0   1
  2 0 201 467
  3 0   0   0
  
  &gt;df2&lt;-data.frame(A=c(201,467),B=c('abc','def'))
      A   B
  1 201 abc
  2 467 def
  </code></pre>
  
  <p>I would like to replace the values in df1 using matching "B" values in df2, creating a dataframe that looks like this: </p>
  
  <pre><code>   A   B   C
  1 NA  NA  NA
  2 NA abc def
  3 NA  NA  NA
  </code></pre>
  
  <p>I can accomplish this on a column by column basis using the following code: </p>
  
  <pre><code>&gt;df2$B[match(df1$B,df2$A)]
  </code></pre>
  
  <p>Unfortunately, I am working with a massive dataset and would therefore prefer to match all of the columns at once. Any help would be much appreciated.</p>