title: Concatenating Row[-1,-3] in the Tidyverse
body: <p>I'm new to the Tidyverse and dplyr and was hoping to get some guidance on how best to concatenate data from row below the current row. For example, in the dataframe below I want to use data in the Grade column to create the data in the Prior3Grades column.  The Prior3Grades data for 1/2/2019 would be created by concatenating the grades from 12/3/18, 11/3/18 and 10/4/18. </p>
  
  <p>Can this be achieved in dplyr using mutate or some other means? Also is this in dplyr's wheelhouse or would this be something better suited to sql.</p>
  
  <p><a href="https://i.stack.imgur.com/5PThF.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/5PThF.png" alt="enter image description here"></a></p>