title: R - group by Date and count different occurrences of value per each day
body: <p>I have a data frame like this:</p>
  
  <pre><code>Title         Date             Priority
  title1        2018-09-03       3 Mid
  title2        2018-09-03       3 Mid
  title3        2018-09-03       3 Mid
  title4        2018-09-03       4 High
  title5        2018-09-03       3 Mid
  title6        2018-09-03       3 Mid
  title7        2018-09-03       3 Mid
  title8        2018-09-03       2 Min
  title9        2018-09-03       3 Mid
  title10       2018-09-03       3 Mid
  title11       2018-09-03       4 High
  title12       2018-09-04       3 Mid
  title13       2018-09-04       3 Mid
  title14       2018-09-04       3 Mid
  title15       2018-09-04       3 Mid
  title16       2018-09-04       3 Mid
  title17       2018-09-04       2 Min
  title18       2018-09-04       3 Mid
  title19       2018-09-04       4 High
  title20       2018-09-04       4 High
  title21       2018-09-04       3 Mid
  title22       2018-09-04       4 High
  title23       2018-09-04       3 Mid
  title24       2018-09-04       3 Mid
  title25       2018-09-04       3 Mid
  title26       2018-09-04       2 Min
  title27       2018-09-04       1 Low
  title28       2018-09-04       3 Mid
  title29       2018-09-05       4 High
  title30       2018-09-05       4 High
  title31       2018-09-05       3 Mid
  title32       2018-09-05       3 Mid
  title33       2018-09-05       3 Mid
  title34       2018-09-05       3 Mid
  title35       2018-09-05       3 Mid
  title36       2018-09-05       3 Mid
  title37       2018-09-05       3 Mid
  </code></pre>
  
  <p>and I'd like to count the number of priority occurrences by day.</p>
  
  <p>In output I'd like to have something like this:</p>
  
  <pre><code>Date         1 Low   2 Min   3 Mid   4 High   5 Critical
  2018-09-03   0       1       8       2        0
  2018-09-04   1       2       11      3        0
  2018-09-05   0       1       10      3        0
  </code></pre>
  
  <p>Is it possible to do it with R?
  I already tried to search a solution but I didn't find one that fits my case. </p>
  
  <p>Thank you all in advance.</p>