Method to extract the title from a ggplot legend

get_legend_title.R

library("visR")

get_legend_title <- function(gg) {
  
  ggb <- ggplot2::ggplot_build(gg)
  ggt <- ggplot2::ggplot_gtable(ggb)
  
  legend_grob_id <- which(sapply(ggt$grobs, function(x) x$name) == "guide-box")
  legend_grob <- ggt$grobs[[legend_grob_id]]
  
  legend_title_id <- which(sapply(legend_grob$grobs[[1]]$layout$name, function(x) x) == "title")
  legend_gtree <- legend_grob$grobs[[1]]$grobs[[legend_title_id]]
  legend_title <- legend_gtree$children[[1]]$children[[1]]$label
  
  return(legend_title)
  
}

gg <- adtte %>%
  visR::estimate_KM("SEX") %>%
  visR::visr()

get_legend_title(gg) #-> "Sex"