title: replacing multiple values with a specific date
body: <p>I have a data frame in R with a column with values from 1 to 711. Each value is repeated multiple times. I want to replace each value with a specific DATE. </p>
  
  <pre><code>df &lt;- data.frame(col1 = c(1,1,1,1,1,2,2,2,4,5,5,2,3) #711 values and total 
        entries = 300000
  df1 &lt;- data.frame(col2 = c("01-01-2014","02-01-2014","03-01-2014",04-01- 
         2014","05-01-2014") #711 unique dates
  
  #Value 1 should be replaced by "01-01-2014"
  #Value 2 should be replaced by "02-01-2014"
  #......
  #Value 711 should be replaced by "12-12-2015"
  </code></pre>