title: Do you use attach() or call variables by name or slicing?
body: <p>Many intro R books and guides start off with the practice of attaching a <code>data.frame</code> so that you can call the variables by name. I have always found it favorable to call variables with <code>$</code> notation or square bracket slicing <code>[,2]</code>. That way I can use multiple <code>data.frame</code>s without confusing them and/or use iteration to successively call columns of interest. I noticed Google recently posted <a href="http://google-styleguide.googlecode.com/svn/trunk/google-r-style.html" rel="nofollow noreferrer">coding guidelines for R</a> which included the line</p>
  
  <blockquote>
    <p>1) attach: avoid using it </p>
  </blockquote>
  
  <p>How do people feel about this practice?</p>