Syntax of `sep =` as separator

Question

I would like to understand how is the syntax of the command sep =. Below, I report an example code:

library(ggpmisc)
library(ggplot2)


formula <- y ~ x + I(x^2)
ggplot(cars, aes(speed, dist)) +
  geom_point() +
  stat_fit_deviations(formula = formula, colour = "red") +
  stat_poly_line(formula = formula) +
  stat_poly_eq(aes(label =  paste(stat(eq.label), stat(adj.rr.label), sep = "*\", \"*")),
               formula = formula)

I understand that sep = "*\", \"*" is aiming to add a comma between eq.label and adj.rr.label. There is no reference on the guide of stat_poly_eq, I would like to understand the meaning of "*\" and \"*", perhaps learning something more to change this configuration.

Answer 1

The labels you create in stat_poly_eq are character strings. They are parsed into expressions, which in turn are converted into plotmath symbols. You can get a feel for how this works if you do:

plot(1:10, type = 'n')
text(5, 5, label = expression(paste(y~`=`~3*italic(x)^2*", "*R^2)))

All the sep is doing in your case is providing a separating comma and space between the formula and the R squared. You can change this to anything you like as long as it parses correctly to a valid plotmath expression:

formula <- y ~ x + I(x^2)
ggplot(cars, aes(speed, dist)) +
  geom_point() +
  stat_fit_deviations(formula = formula, colour = "red") +
  stat_poly_line(formula = formula) +
  stat_poly_eq(aes(label =  paste(stat(eq.label), stat(adj.rr.label), 
                                  sep = "*\" is the formula, and the R squared is \"*")),
               formula = formula)

See ?plotmath to find out all the things your can do with plotmath expressions