title: Running complex functions per row
body: <p>I would like to use complex functions in a nested data frame.</p>
  
  <p>My data looks like this:</p>
  
  <pre><code>Name     Date
  John     01.01.
  Mark     03.09.
  Edith    03.04.
  Edith    08.08.
  Mark     04.01.
  Edith    01.03.
  John     01.03.
  John     01.04.
  Mark     02.03.
  Edith    04.05.
  Edith    07.05.
  Mark     04.02.
  Edith    09.01.
  John     01.09.
  
  </code></pre>
  
  <p>In a new column Day, For each name, I would like to know the number of days between a given Date row and the earliest date for that person.</p>
  
  <p>So that John will look like:</p>
  
  <pre><code>Day
  0
  ..
  2
  2
  ..
  9
  </code></pre>
  
  <p>I am experimenting with nest(), then running a function with modfiy, but I am very new to R, and it doesn't work I and looks don't really understand what even the problem is.</p>
  
  <p>Thanks for help!</p>