Home How to use mapply on stat_poly_eq (i.e. equation and R-squared values) in ggplot2 R?

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How to use mapply on stat_poly_eq (i.e. equation and R-squared values) in ggplot2 R?

April 14, 2022

I am trying to add the R-squared equations, each with a different formula. I tried the mapply function modelling on a previous answer but nothing happens. There is no error, but not equation displayed either. I also want to plot the equation on one line, and the Rsquared in the next line, I don’t know where exactly to add the \n in the stat_poly_eq.

library(ggplot2)
library(ggpmisc)
set.seed(14)
df <- data.frame(
  var.test = c("T","T","T","T","M","M","M","M","A","A","A","A"),
  val.test = rnorm(12,8,5),
  x = c(1:12)
)

my.formula <- c(y~x + I(x^2), y~x, y~x + I(x^2))
ggplot(df, aes(x = x, y = val.test)) + 
  geom_point() +
  mapply(function(x, z) geom_smooth(method="glm", data=function(d) subset(d, var.test==z), formula = x, 
                                    method.args = list(family = "poisson"), color = "black" ), my.formula, c("A","M","T")) + facet_grid(.~var.test) + 
  mapply(function(x,z) stat_poly_eq(formula = x, aes(label = paste(..eq.label.., ..rr.label.., sep = "~~~")),  parse = TRUE, size = 2.5, col = "black", data=function(d) subset(d, var.test==z),my.formula, c("A","M","T")))

>Solution :

The issue with your code was a wrong closing paranthesis, i.e. you included my.formula and c("A","M","T") as arguments of stat_poly_eq. That’s why no labels were plotted as you looped over nothing.

Concerning your second question. TBMK you can’t have a line break in a math expression. One approach to deal with that would be to add the equation and the R^2 via two separate stat_poly_eq layers.

Additionally I simplified your code a bit. It’s not necessary to have multiple mapplys. One is sufficient. You could return multiple layers by wrapping them inside a list.

library(ggplot2)
library(ggpmisc)

ggplot(df, aes(x = x, y = val.test)) +
  geom_point() +
  mapply(function(x, z) {
    data <- subset(df, var.test == z)
    list(
      geom_smooth(
        method = "glm", data = data, formula = x,
        method.args = list(family = "poisson"), color = "black"
      ),
      stat_poly_eq(formula = x, aes(label = ..eq.label..), 
                   parse = TRUE, size = 2.5, col = "black", data = data, vjust = -0.1),
      stat_poly_eq(formula = x, aes(label = ..rr.label..), 
                   parse = TRUE, size = 2.5, col = "black", data = data, vjust = 1.1)
    )
  }, my.formula, c("A", "M", "T")) +
  facet_grid(. ~ var.test)