A ggplot2 scale that can handle a data frame column

scale_df.R

library(ggplot2)

ScaleDataFrame <- ggproto(
  "ScaleDataFrame", Scale,
  aesthetics = NULL,
  plot_env = emptyenv(),
  scales_list = ggproto(NULL, ggplot2:::ScalesList),
  
  transform = function(self, x) {
    x[] <- purrr::map2(
      names(x), x, 
      function(col_name, col) self$get_scale(x, col_name)$transform(col)
    )
    x
  },
  
  train = function(self, x, ...) {
    purrr::walk2(
      names(x), x, 
      function(col_name, col) self$get_scale(x, col_name)$train(col, ...)
    )
  },
  
  map = function(self, x, ...) {
    x[] <- purrr::map2(
      names(x), x, 
      function(col_name, col) self$get_scale(x, col_name)$map(col, ...)
    )
    x
  },
  
  get_scale = function(self, df, col) {
    fake_aesthetics <- paste0(self$aesthetics, ":::", col)
    
    if (is.null(self$scales_list$get_scales(fake_aesthetics[1]))) {
      scale <- ggplot2:::find_scale(self$aesthetics[1], df[[col]], self$plot_env)
      scale$aesthetics <- fake_aesthetics
      self$scales_list$add(scale)
    }
    
    self$scales_list$get_scales(fake_aesthetics[1])
  },
  
  clone = function(self) {
    ggproto(NULL, self, scales_list = self$scales_list$clone())
  }
)