title: Calculating standard deviation for each row on selected columns
body: <p>I am not used to R, so to practice I am trying to do everything that I used to do on SPSS on R.</p>
  
  <p>In my dataset each row is a case. The columns are survey questions (1 per question). </p>
  
  <p>Say I have columns "A1" up to "A6", "B1" to "B6" and so on  </p>
  
  <p>I just finished calculating the mean for each person on A1 to A6 </p>
  
  <p><code>data$meandata &lt;-  rowMeans(subset(data, select=c(A1:A6), na.rm=TRUE))
  </code> </p>
  
  <p>How do I calculate the standard deviation of <code>meandata</code> ?</p>