plotting 3 variables on a single plot in ggplot2 - r

Question

Hi have an experiment which consists of three variables, and I would like to plot them all on a single plot.
This is my df:
AB <- data.frame(block=c("A", "A", "A", "A", "B", "B", "B", "B" ),
familiarity=c("fam", "fam", "unfam", "unfam" ),
prime=c("P", "UP" ),
RT=c("570.6929", "628.7446", "644.6268", "607.4312", "556.3581", "645.4821", "623.5624", "604.4113"))
Right now I can only break one of the variables into two separate plots, like this where A and B are the two levels of the third variable:
A <- AB[which(AB$block == "A"),]
B <- AB[which(AB$block == "B"),]
pa <- ggplot(data=A, aes(x=prime, y=RT, group=familiarity)) +
geom_line(aes(linetype=familiarity), size=1) +
expand_limits(y=c(500,650))
pb <- ggplot(data=B, aes(x=prime, y=RT, group=familiarity)) +
geom_line(aes(linetype=familiarity), size=1) +
expand_limits(y=c(500,650))
I would like to superimpose plot A over plot B, and have this third variables to be identified by color.
Any ideas?

Answer 1

Is this what you mean?
p_all <- ggplot(AB, aes(x=prime,y=RT,group=interaction(familiarity,block))) +
geom_line(aes(linetype=familiarity,color=block))
Data used:
AB <- structure(list(block = structure(c(1L, 1L, 1L, 1L, 2L, 2L, 2L,
2L), .Label = c("A", "B"), class = "factor"), familiarity = structure(c(1L,
1L, 2L, 2L, 1L, 1L, 2L, 2L), class = "factor", .Label = c("fam",
"unfam")), prime = structure(c(1L, 2L, 1L, 2L, 1L, 2L, 1L, 2L
), class = "factor", .Label = c("P", "UP")), RT = c(570.6929,
628.7446, 644.6268, 607.4312, 556.3581, 645.4821, 623.5624, 604.4113
)), .Names = c("block", "familiarity", "prime", "RT"), row.names = c(NA,
-8L), class = "data.frame")

Answer 2

IF you have different datasets for those variables, then you can specify the data
ggplot()+
geom_line(data=A, aes(x=prime, y=RT, group=familiarity,linetype=familiarity), size=1) +
geom_line(data=B, aes(x=prime, y=RT, group=familiarity,linetype=familiarity), size=1)+
expand_limits(y=c(500,650))