title: Combining two variables based on a specific condition R
body: <p>I have a problem, which should not be difficult but given my rudimentary knowledge of R,I am getting stuck. Any help is appreciated (especially a dplyr one :).</p>
  <p>Let's say I have two dataframes df and df_new. Now df has 20 observations and df_new has 7 observations, I want to create a new column in dataframe df such that it takes the values from df_new$x. Since df has more observations than df_new, the values should be repeated based on a match between df$let and df_new$let1.</p>
  <pre><code>set.seed(7)
  df &lt;- data.frame(x=runif(20),let=rep(letters[1:10],each=2))
  df_new &lt;- data.frame(x=runif(7),let1=c('a','b','b','c','d','e','e'))
  </code></pre>