title: R question. 'scatterplot' function in 'car' library. "object is not a matrix" error
body: <p>Any ideas why I am getting an error with the following code?</p>
  
  <p>Thanks in advance!   </p>
  
  <pre><code>library(lattice)
  library(car)
  
  set.seed(1234)
  response=round(rnorm(60),2)
  explanatory&lt;-round(c(rnorm(20, 10,1), rnorm(10, 8, 1), rnorm(10,20,1), rnorm(20,18,1)),2)
  gender=c(rep("male", 30), rep("female", 30))
  factor1=as.factor(c(rep('a', 20), rep('b', 20), rep('c', 20)))
  scatterplot(response~explanatory, smooth=FALSE, reg.line=FALSE)
  </code></pre>