title: Add a date column to a data frame
body: <p>I am fairly new to R and I am trying to create a loop to add date column in my data frame that increases by day to a set date.</p>
  
  <p>My data looks like this:</p>
  
  <pre><code>'A'  'B'  'C'
   1    2    3
   1    2    3
   4    5    6
   4    5    6
  </code></pre>
  
  <p>I am trying to add a date column so the data looks like this:</p>
  
  <pre><code>'A'  'B'  'C'  'Date'
   1    2    3    1/1
   1    2    3    1/1
   4    5    6    1/1
   4    5    6    1/1
   1    2    3    1/2
   1    2    3    1/2
   4    5    6    1/2
   4    5    6    1/2
   1    2    3    1/3
   1    2    3    1/3
   4    5    6    1/3
   4    5    6    1/3
  </code></pre>
  
  <p>I appreciate any help!</p>