title: ranking date in R
body: <p>I  have a dataframe of two columns TSH values and dates.
  I want to give a rank number for each day (1 starting from the oldest date) as in the picture.</p>
  <p><a href="https://i.stack.imgur.com/0ofv1.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/0ofv1.png" alt="enter image description here" /></a></p>