title: r, does not equal, nas are not included
body: <p>I'm trying to filter my data to leave out certain values.  The problem is that I want to include the NAs.  When I use the does not equal, "!=", operator, the NAs are also removed.</p>
  
  <pre><code>    a= c("A","C","B",NA,"C","A",NA,"B","A")
      df = data.frame(a)
  
      df2 &lt;- df %&gt;%
         filter(a != "B")
      df2
  </code></pre>
  
  <p>For example, I would like df2 to include everything not equal to B (A and C) and NA instead of only A and C.</p>