title: Getting error in R trying to calculate mean on column that contains NA
body: <p>From searching online and in this group, it seems like this should work:</p>
  
  <pre><code>&gt; mean(r_lab$ozone, na.rm=TRUE)
  </code></pre>
  
  <p>However, what I get is:</p>
  
  <pre><code>[1] NA
  Warning message:
  In mean.default(r_lab$ozone, na.rm = TRUE) :
    argument is not numeric or logical: returning NA
  </code></pre>
  
  <p><strong>This is the contents of that column in the dataset:</strong></p>
  
  <pre><code>&gt; r_lab$Ozone
   [1]  41  36  12  18  NA  28  23  19   8  NA   7  16  11  14
  [15]  18  14  34   6  30  11   1  11   4  32  NA  NA  NA  23
  </code></pre>
  
  <p>I'm sort of flustered. </p>