title: Warning error of "plot.new has not been called yet" when attempting to plot ecdf for a variable
body: <p>I am having difficulty plotting an <code>ECDF</code> function for a variable.  The simple code below provides an example;</p>
  
  <pre><code>A = rnorm(100)
  plot(ecdf(A),
       abline(v=c(-1,1,1.5)))
  </code></pre>
  
  <p>When I attempt to plot the function with vertical lines the warning message </p>
  
  <blockquote>
    <p>Error in int_abline(a = a, b = b, h = h, v = v, untf = untf, ...) :<br>
    plot.new has not been called yet</p>
  </blockquote>
  
  <p>appears.</p>
  
  <p>I have searched a number of sources but I have not been able to identify what mistake I am making.  If anyone could provide information on how to plot these <code>ecdf</code> plots and then add vertical lines I would greatly appreciate it.</p>
  
  <p>Thanks.</p>