title: Subset function not removing NAs
body: <p>I have a data frame like this:</p>
  
  <pre><code>df
  
  Date     Player Injured
  1/2/2012      A      No
  1/3/2012      B     Yes
  1/4/2012      C      No
  1/5/2012      B      NA
  1/5/2012      A      No
  1/7/2012      B     Yes
  1/8/2012      A      No
  1/3/2012      B     Yes
  1/2/2012      D      No
  1/3/2012      F      NA
  </code></pre>
  
  <p>I am trying to use subset function to select players that injury info is NA:</p>
  
  <pre><code>x &lt;- subset(df, injured!="NA")
  </code></pre>
  
  <p>x data frame is not populating. It seems very straightforward. Any ideas what I am doing wrong here?</p>