title: How to add missing dates to a column with NA's to the other columns?
body: <pre><code>         Date NewArea.km2 IDday
  1  2018-03-01    152.3972     0
  2  2018-03-15    152.3972     0
  3  2018-04-01    152.3972     0
  4  2018-04-15    152.3972     0
  5  2018-05-01    152.3972     0
  6  2018-05-15    152.3972     0
  7  2018-06-01    152.3972     0
  8  2018-06-10    152.3972     0
  9  2018-06-15    152.3972     0
  10 2018-06-20    152.3972     0
  11 2018-06-21    152.3972     1
  12 2018-06-22    152.3972     3
  13 2018-06-23    152.3972     4
  14 2018-06-24    152.3972     6
  15 2018-06-25    152.3972     6
  16 2018-06-26    152.3972    16
  17 2018-06-27    152.3972    22
  18 2018-06-28    152.3972    22
  19 2018-06-29    152.3972    24
  20 2018-06-30    152.3972    24
  21 2018-07-01    152.3972    27
  </code></pre>
  
  <p>Here's a subset of the data I have. As you may have eluded to from the title, I would like to add rows to my data frame such that missing dates are also included (i.e. 2018-03-02, 2018-03-03, etc.) The other two columns ideally would fill up with NA's such that the new row 2 would read </p>
  
  <pre><code>2  2018-03-02  NA  NA
  </code></pre>