title: Is there a way to select and proportion rows based on their value in R?
body: <p>I have a dataframe which looks like this:</p>
  <pre><code>   a          b  c   d
  1  2005-01-01 0 ... ...
  2  2005-02-22 1 ... ...
  3  2005-04-02 0 ... ...
  4  2005-12-01 3 ... ...
  5  2006-03-03 0 ... ...
  6  2006-06-08 1 ... ...
  7  2006-10-11 0 ... ...
  8  2006-12-02 4 ... ...
  9  2007-03-24 0 ... ...
  10 2007-04-06 2 ... ...
  11 2008-01-28 0 ... ...
  12 2008-08-19 0 ... ...
  13 2008-09-12 0 ... ...
  14 2008-12-12 2 ... ...
  15 2009-05-27 0 ... ...
  16    ...     . ... ...
  </code></pre>
  <p>And I want to select all the rows in the year 2005 and view how many of them are 0,1,2,3 or 4 for example (so combined with column b). Maybe with proportions? For example that the result would be:</p>
  <pre><code>output:
  2005
  0    1    2    3    4
  20%  20%  20%  20%  20%
  </code></pre>
  <p>I tried <code>table(year(DF$a), c=DF$b)</code> however this only yields an overview of all the years, and no proportions or anything like that. I tried piping this into a proportions function with <code>%&gt;%</code>, however this doesn't work.</p>
  <p>Anyone know how to do this?</p>