title: Removal of constant columns in R
body: <p>I was using the prcomp function when I received this error</p>
  
  <pre><code>Error in prcomp.default(x, ...) : 
  cannot rescale a constant/zero column to unit variance
  </code></pre>
  
  <p>I know I can scan my data manually but is there any function or command in R that can help me remove these constant variables?
  I know this is a very simple task, but I have never been across any function that does this.</p>
  
  <p>Thanks,</p>