Does using geom_abline(...) (as well as geom_vline and geom_hline) result in multiple overplotting of the same line when used "naively"?
For example, say we are interested in the following faceted scatterplot:
library(ggplot2)
library(dplyr)
k <- 4
data.frame(id = letters[1:k],
m = rnorm(k),
b = rnorm(k))[rep(1:k, 30),] %>%
mutate(x = rnorm(n()),
eps = 0.1*rnorm(n()),
y = m*x + b + eps) %>%
ggplot(aes(x, y)) +
geom_point() +
facet_wrap(~ id) ->
p
The easiest way to add an ab-line to it is as follows:
print(p + geom_abline(aes(slope = m, intercept = b), color = 'red'))
Is that the "right way" to do it? In particular, doesn't the above plot the ab-line 30 times in each facet? For example this makes it seem like it does:
print(p + geom_abline(aes(slope = m, intercept = b + eps), color = 'red'))
If so, is it better to do something like this?
print(p + geom_abline(aes(slope = m, intercept = b),
data = Z %>% group_by(id) %>% summarize(m = unique(m), b = unique(b)),
color = 'red'))
Note that this produces something visually indistiguishable from the first plot. My question is about the right way to use these ggplot functions.