plotting two vectors of data on a GGPLOT2 scatter plot using R

Answer 1

well after posting the question I ran across this R Help thread that may have helped me. It looks like I can do this:

 pg + geom_line(data=dd,aes(x_value, Actual_value,group=State_CD), colour="green")

is that a good way of doing things? It odd to me because adding the second item has a totally different syntax than the first.

Answer 2

you might just want to change the form of your data a little bit, so that you have one y-axis variable, with an additional factor variable indicating whether it is a predicted or actual variable.

Is this something like what you are trying to do?

dd<-data.frame(type=rep(c("Predicted_value","Actual_value"),20),y_value=rnorm(40),
       x_value=rnorm(40),State_CD=rnorm(40)>0)
qplot(x_value,y_value,data=dd,colour=type,facets=.~State_CD)

Answer 3

I'm sure Hadley will have a better answer, but - the syntax is different because the ggplot(dd,aes()) syntax is (I think) primarily intended for plotting just one variable. For two, I would use:

ggplot() + 
geom_point(data=dd, aes(x_value, Actual_value, group=State_CD), colour="green") + 
geom_point(data=dd, aes(x_value, Predicted_value, group=State_CD), shape = 2) + 
facet_wrap(~ State_CD) + 
opts(aspect.ratio = 1)

Pulling the first set of points out of the ggplot() gives it the same syntax as the second. I find this easier to deal with because the syntax is the same and it emphasizes the "Grammar of Graphics" that is at the core of ggplot2.