title: Replicate a given value for each ID in R
body: <p>I have a dataset like this:</p>
  
  <pre><code>ID     DATE     NUMBER
  1    01-01-20     1
  1    15-01-20     2
  1    24-02-20     3
  2    15-03-20     1
  2    20-04-20     2
  2    01-05-20     3
  </code></pre>
  
  <p>and I want to add a new column that replicate the value of the first date for each ID, like:</p>
  
  <pre><code>ID     DATE     NUMBER   NEW_DATE
  1    01-01-20     1      01-01-20
  1    15-01-20     2      01-01-20
  1    24-02-20     3      01-01-20
  2    15-03-20     1      15-03-20
  2    20-04-20     2      15-03-20
  2    01-05-20     3      15-03-20
  </code></pre>
  
  <p>How can I do it?
  Thanks everyone</p>