title: How to remove subjects with missing yearly observations in R?
body: <pre><code>     num Name  year   age       X 
  1      1   A   2011    68  116292
  2      1   A   2012    69   46132
  3      1   A   2013    70    7042
  4      1   A   2014    71 -100425
  5      1   A   2015    72    6493
  6      2   B   2011    20   -8484
  7      3   C   2015    23 -120836
  8      4   D   2011     3  -26523
  9      4   D   2012     4    9923
  10     4   D   2013     5   82432
  </code></pre>
  
  <p>I have the data which is represented by various subjects in 5 years. I need to remove all the subjects, which are missing any of years from 2011 to 2015. How can I accomplish it, so in given data only subject A is left?</p>