avoid zig-zag pattern in quadratic fit in ggplot

Question

I struggle with plotting a quadratic fit in ggplot, as the line between the overlapping x-values jumps back and forth between the upper and lower side of the curve.

However, doing the same in base plot, it works, which makes me think I am overlooking something (possibly really stupid) in ggplot. Could anybody guide me towards how to receive a propper line in ggplot?

I unfortunately don`t know how to reproduce the exact problem, so just add code for a similar shaped "curve":

library(ggplot2)
x1 <- log(c(1:100, 99:1))
y1 <- log(seq(0.22, 0.2, length.out = 199))
dat <- data.frame(x = x1, y = y1)
ggplot(data = dat, aes(x = x, y = y)) + geom_line()
plot(y1 ~ x1, type = "l")

Thanks a lot in advance!

Answer 1

Try geom_path() instead.

library(ggplot2)
x1 <- log(c(1:100, 99:1))
y1 <- log(seq(0.22, 0.2, length.out = 199))
dat <- data.frame(x = x1, y = y1)
ggplot(data = dat, aes(x = x, y = y)) + geom_path()
plot(y1 ~ x1, type = "l")

geom_path() connects the observations in the order in which they appear in the data. geom_line() connects them in order of the variable on the x axis. Documentation.