is geom_line()?

[Marcell]

Is there a way to get to know if a ggplot object is based on geom_line?

goal: I want to write a function which adds additional object to a ggplot figure if it is a line graph.

Thank you for your answer,
Marcell

[mattwarkentin]

This is kind of a hacky solution to check whether a ggplot object contains a layer with the class GeomLine. The function has_geom_line() iterates over the layers to check class inheritance. It returns TRUE if any layers are geom_line(), FALSE otherwise.

library(ggplot2)
library(magrittr)

has_geom_line <- function(plot) {
  stopifnot(is.ggplot(plot))
  any(purrr::map_lgl(plot$layers, ~inherits(.x$geom, "GeomLine")))
}

p <- 
  mtcars %>% 
  ggplot(aes(hp, mpg)) +
  geom_line() +
  geom_point()

has_geom_line(p)
#> [1] TRUE