在 R 中使用 ggplot2 向二维密度图添加一条线

Question

Here is 2D density plot from Hadley Wickham's book:

f2d <- with(faithful, MASS::kde2d(eruptions, waiting, 
                                  h = c(1, 10), n = 50))
df <- with(f2d, cbind(expand.grid(x, y), as.vector(z)))
names(df) <- c("eruptions", "waiting", "density")
erupt <- ggplot(df, aes(waiting, eruptions, fill = density)) +
   geom_tile() +
   scale_x_continuous(expand = c(0, 0)) + 
   scale_y_continuous(expand = c(0, 0))
erupt + scale_fill_gradient(limits = c(0, 0.04), low = "white", high = "black") 

I try to plot a line on top of this:

mydf <- data.frame(x=c(50,60,70),y=c(2,3,4))
erupt + scale_fill_gradient(limits = c(0, 0.04), low = "white", high = "black") + geom_line(aes(x=x,y=x), data = mydf)

But I get the following error:

Error in data.frame(x = c(50, 60, 70), y = c(50, 60, 70), fill = function (x,  : 
  arguments imply differing number of rows: 3, 0

I don't understand why this is. Thank you.

Answer 1

Two problems, first as @aosmith says you need to set density specific to the aesthetic in geom_tile. secondly there's a typo in geom_line(aes(x=x,y=x)

So

erupt <- ggplot(df, aes(waiting, eruptions)) +
  geom_tile(aes(fill=density)) +
  scale_x_continuous(expand = c(0, 0)) + 
  scale_y_continuous(expand = c(0, 0))

mydf <- data.frame(x=c(50,60,70),y=c(2,3,4))
erupt + scale_fill_gradient(limits = c(0, 0.04), low = "white", high = "black") + 
  geom_line(aes(x=x,y=y), data = mydf)

Produces