title: "Error: Continuous value supplied to discrete scale" in default data set example mtcars and ggplot2
body: <p>I am trying to replicate <a href="http://www.sthda.com/english/wiki/ggplot2-scatter-plots-quick-start-guide-r-software-and-data-visualization#change-the-point-colorshapesize-manually" rel="noreferrer">the example here (sthda.com)</a> using the following code:</p>
  
  <pre><code># Change point shapes and colors manually
  ggplot(mtcars, aes(x=wt, y=mpg, color=cyl, shape=cyl)) +
    geom_point() + 
    geom_smooth(method=lm, se=FALSE, fullrange=TRUE)+
    scale_shape_manual(values=c(3, 16, 17))+ 
    scale_color_manual(values=c('#999999','#E69F00', '#56B4E9'))+
    theme(legend.position="top")
  </code></pre>
  
  <p>The example on that web page says that code should produce the following result: </p>
  
  <p><img src="https://i.stack.imgur.com/y4xaN.png" alt="plot"></p>
  
  <p>But when I run it in R, I get the following error:</p>
  
  <blockquote>
    <p>"Error: Continuous value supplied to discrete scale"</p>
  </blockquote>
  
  <p>Does anyone know what could be wrong with this code? Or why I am getting a different result than the example?</p>
  
  <p>If someone could run the sample code and tell me if they get the same error I would be very grateful.</p>