title: Getting "NA" when I run a standard deviation
body: <p>Quick question. I read my csv file into the variable <code>data</code>. It has a column label <code>var</code>, which has numerical values.</p>
  
  <p>When I run the command </p>
  
  <pre><code>sd(data$var)
  </code></pre>
  
  <p>I get </p>
  
  <pre><code>[1] NA 
  </code></pre>
  
  <p>instead of my standard deviation. </p>
  
  <p>Could you please help me figure out what I am doing wrong?</p>