ggplot: (manually) create legend when referencing different data.frames - r

Question

Ok, lets take some sample data.
A <- sample(1:100, 25)
B <- sample(1:25, 25)
df.1 <- data.frame(A,B)
C <- sample(1:80, 15)
D <- sample(1:15, 15)
df.2 <- data.frame(C,D)
Then we plot the data using ggplot
library(ggplot2)
(plot2 <- ggplot(NULL) +
geom_point(data=df.1, aes(x=A, y=B),
color='black', cex=1, pch=16 ) +
geom_smooth(data=df.1, aes(x=A, y=B), method="lm", size=1,
se=FALSE, colour="black", linetype=2)+
geom_point(data=df.2, aes(x=C, y=D),
color='black', cex=1, pch=15 ) +
geom_smooth(data=df.2, aes(x=C, y=D), method="lm", size=1,
se=FALSE, colour="black", linetype=1)+
scale_y_continuous("Y scale") +
ggtitle("Plot") +
theme_bw()+
theme(plot.title = element_text(face="bold", size=20),
axis.title.x = element_text(vjust=-0.25),
axis.title.y = element_text(vjust=1),
axis.title = element_text(face="bold", size=15)
)
)
So we have created and modified the title, axis, etc.
But I want to create a legend which shows the linetype's from the geom_smooth() function of df.1 and df.2. It should be in the top right of the graph.
(so for df.1 we want a solid line and df.2 a dashed line)
The example here walks you through an example, but the data comes from within the same data set

Answer 1

Here you go:
#combine and create x and y (as mappings follow
#same pattern)
df.1$group <- "df.1"
df.1$x <- df.1$A
df.1$y <- df.1$B
df.2$group <- "df.2"
df.2$x <- df.2$C
df.2$y <- df.2$D
library(plyr) #for rbind.fill
df.all <- rbind.fill(df.1,df.2)
plot3 <- ggplot(df.all, aes(x=x,y=y,group=group)) +
geom_point(color='black', cex=1, pch=16 ) +
geom_smooth(aes(linetype=group),method="lm", size=1,
se=FALSE, colour="black") +
scale_y_continuous("Y scale") +
ggtitle("Plot") +
theme_bw()+
theme(plot.title = element_text(face="bold", size=20),
axis.title.x = element_text(vjust=-0.25),
axis.title.y = element_text(vjust=1),
axis.title = element_text(face="bold", size=15)
) +
#add custom linetypes (not necessary now, as default mapping to 1 and 2)
plot3 + scale_linetype_manual(values=c("df.1"=1,"df.2"=2))