title: ggplot2 using open or closed circles
body: <p>I have data like this (4703 lines):</p>
  
  <pre><code>a   b
  100 1
  101 0
  102 0
  103 1
  104 1
  </code></pre>
  
  <p>I want to create a graph of circles, that plots the position and whether the position is 1 (black circle) or 0 (white circle).  I've been trying to play around with the following code:</p>
  
  <pre><code>data &lt;- read.csv("/Users/Steve/Desktop/binary.csv")
  ggplot(data, aes(x=a, y=b)) + 
  +     geom_point(aes(shape=b)))
  </code></pre>
  
  <p>I keep getting the following error:</p>
  
  <blockquote>
    <p>Error: A continuous variable can not be mapped to shape</p>
  </blockquote>