r adding line (new coordinates) to ggplot2 scaterplot

r ggplot2

How can I add a line with new x coordinates to my scatterplot? I get an error saying the line x-values must match those from my scatterplot.. I tried using geom_line() as you can see

library(ggplot2)

x <- c(1,2,3)
y <- c(4,5,6)

a <- seq(0.5,5, by = 0.5)
b <- seq(1,10)


ggplot(as.data.frame(cbind(x,y)), aes(x, y)) +
  geom_point(shape = 1) +
  geom_point(aes(2.5,2.5, colour = "My Portfolio"), 
             shape = 18, 
             size = 3) +
  geom_line(aes(a, b)) +
  ggtitle("Efficient Frontier") +
  xlab("Volatility (Weekly)") +
  ylab("Expected Returns (Weekly)") +
  theme(plot.title = element_text(size=14, face="bold.italic", hjust = 0.5, margin=margin(0,0,15,0)),
        axis.title.x = element_text(size = 10, margin=margin(15,0,0,0)),
        axis.title.y = element_text(size = 10, margin=margin(0,15,0,0)),
        panel.border = element_rect(colour = "black", fill=NA, size=1),
        legend.position = c(0.93,0.06),
        legend.title = element_blank(),
        legend.text = element_text(size=8),
        legend.background = element_rect(color = "black"),
        legend.key=element_blank())

thanks!

You have to provide a new data.frame to geom_line() and set the aestetics accordingly.

library(ggplot2)

x <- c(1,2,3); y <- c(4,5,6)
a <- seq(0.5,5, by = 0.5); b <- seq(1,10)

ggplot(as.data.frame(cbind(x,y)), aes(x, y)) +
  geom_point(shape = 1) +
  geom_point(aes(2.5,2.5, colour = "My Portfolio"), 
             shape = 18, 
             size = 3) +
  geom_line(data=data.frame(a,b), mapping=aes(x=a, y=b)) +
  ggtitle("Efficient Frontier") +
  xlab("Volatility (Weekly)") +
  ylab("Expected Returns (Weekly)") +
  theme(plot.title = element_text(size=14, face="bold.italic", hjust = 0.5, margin=margin(0,0,15,0)),
        axis.title.x = element_text(size = 10, margin=margin(15,0,0,0)),
        axis.title.y = element_text(size = 10, margin=margin(0,15,0,0)),
        panel.border = element_rect(colour = "black", fill=NA, size=1),
        legend.position = c(0.93,0.06),
        legend.title = element_blank(),
        legend.text = element_text(size=8),
        legend.background = element_rect(color = "black"),
        legend.key=element_blank())

enter image description here