clustered.dotplots(xgroup, ygroup, freq, type = "circles",
 main="",xlab="",ylab="",x_las=1,y_las=1,axes=TRUE,size=1,...)

df <- structure(list(set = c("09t0101 TJ", "09t0102 MW", "09t0201 EH", 
 "09t0202 NH", "09t0101 TJ", "09t0102 MW", "09t0201 EH", "09t0202 NH", 
 "09t0101 TJ", "09t0102 MW", "09t0201 EH", "09t0202 NH", "09t0101 TJ", 
 "09t0102 MW", "09t0201 EH", "09t0202 NH", "09t0202 NH"), grade = c("1", 
 "1", "1", "1", "2", "2", "2", "2", "3", "3", "3", "3", "4", "4", 
 "4", "4", "5"), freq = c(7, 8, 2, 3, 11, 4, 11, 3, 3, 8, 3, 8, 
 3, 9, 3, 2, 5)), .Names = c("set", "grade", "freq"), row.names = c(NA, 
 17L), class = "data.frame")
 clustered.dotplots(xgroup = df$set, ygroup = df$grade, freq = df$freq)
 clustered.dotplots(xgroup = df$set, ygroup = df$grade, freq = df$freq,
  col = "gray")
 clustered.dotplots(xgroup = df$set, ygroup = df$grade, freq = df$freq,
  type = "points")
 clustered.dotplots(xgroup = df$set, ygroup = df$grade, freq = df$freq,
  type = "points", pch = 19, col = "red")
 # this will cause an error
 # clustered.dotplots(xgroup = mtcars$cyl, ygroup = mtcars$gear,
 #  freq = mtcars$carb)
 # how to fix it
 cumcars<-by(mtcars$carb,list(mtcars$cyl,mtcars$gear),valid.n)
 mtcars2<-data.frame(cyl=NA,gear=NA,carb=NA)
 rownum<-1
 for(cyl in dimnames(cumcars)[[1]]) {
  for(gear in dimnames(cumcars)[[2]]) {
   if(!is.na(cumcars[cyl,gear])) {
    mtcars2[rownum,]<-c(as.numeric(cyl),as.numeric(gear),cumcars[cyl,gear])
    rownum<-rownum+1
   }
  }
 }
 clustered.dotplots(xgroup = mtcars2$cyl, ygroup = mtcars2$gear,
  freq = mtcars2$carb,main="Cars by number of cylinders and gears",
  xlab="Number of cylinders",ylab="Number of gears",type="points",pch=5)