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rggplot2ggpmisc

Is there a way to add number of observations to plot label using ggpmisc::stat_poly_eq

x <- 1:100
y <- (x + x^2 + x^3) + rnorm(length(x), mean = 0, sd = mean(x^3) / 4)
my.data <- data.frame(x = x, y = y,
                      group = c("A", "B"),
                      y2 = y * c(0.5,2),
                      w = sqrt(x))

formula <- y ~ poly(x, 3, raw = TRUE)

ggplot(my.data, aes(x, y)) +
  geom_point() +
  geom_smooth(method = "lm", formula = formula) +
  stat_poly_eq(formula = formula, parse = TRUE)

like so:

enter image description here

Solution 
  • ggplot(my.data, aes(x, y)) +
  geom_point() +
  geom_smooth(method = "lm", formula = formula) + 
  ggpmisc::stat_poly_eq(aes(label = paste(stat(rr.label), paste("N ~`=`~", nrow(my.data)), sep = "*\", \"*")), formula = formula, parse=T)

    You can include additional text with aes. Since the string is parsed you have to escape the equals sign with ~`=`~.

    Edit: With faceting

    You can create an additional unused mapping of group row counts to be used as a variable in the paste statement in lieu of nrow(my.data).

    ggplot(my.data %>% group_by(group) %>% mutate(n = n()), aes(x, y, n = n)) +
  geom_point() +
  geom_smooth(method = "lm", formula = formula) +
  facet_grid(vars(group)) + 
  ggpmisc::stat_poly_eq(aes(label = paste(stat(rr.label), paste("N ~`=`~", n), sep = "*\", \"*")), 
                        formula = formula, parse=T)