R/abstract_stat.R

In ggdist: Visualizations of Distributions and Uncertainty

# A stat base class designed to reduce boilerplate
#
# Author: mjskay
###############################################################################



# AbstractStat ------------------------------------------------------------

#' Stat base class designed to reduce boilerplate
#'
#' A base class for orientation-aware stats that handles boilerplate generation
#' (e.g. for default parameter values). Should never be created on its own,
#' only used as a base class.
#'
#' Differences from ggplot2::Stat:
#'
#' - It is assumed that child classes will use `compute_panel()` and not
#' `compute_group()`, so parameter names are always auto-detected from `compute_panel()`.
#' - A `default_params` property is used to hold a list mapping from parameters
#' onto their default values (used in boilerplate generation). This list is also
#' used instead of `extra_params` in `parameters()` to auto-detect parameters.
#' These default values are also automatically applied in `setup_params()`.
#' - An `orientation_options` property provides parameters passed to `get_flipped_aes()`.
#' Necessary orientation detection boilerplate is included in `setup_params()` and
#' `setup_data()`.
#' - `hidden_params` provides a list of parameters not to be exposed in the
#' `stat_XXX()` constructor
#' - `deprecated_params` provides a list of deprecated parameters that will cause
#' a warning to be generated if used.
#' - `layer_args` provides a list of layer arguments (such as `show.legend` and
#' `inherit.aes`) and their default values.
#'
#' @keywords internal
#' @noRd
AbstractStat = ggproto("AbstractStat", Stat,

  ## aesthetics --------------------------------------------------------------

  # named list: aesthetic => doc string
  aes_docs = list(),

  get_aes_docs = function(self, ...) {
    self$aes_docs
  },

  # aesthetics to hide from documentation
  hidden_aes = character(),


  ## layer function ----------------------------------------------------------

  # layer function to use to construct the layer --- default is ggplot2::layer()
  layer_function = "layer",

  # arguments passed to the stat_XXX() constructor and the underlying layer() call
  layer_args = list(
    show.legend = NA,
    inherit.aes = TRUE
  ),


  ## params ------------------------------------------------------------------

  default_params = list(
    orientation = NA,
    na.rm = FALSE
  ),

  # parameters to hide from user input in the stat_XXX() constructor
  hidden_params = character(),

  # parameters that have been deprecated and which should throw a warning if used
  deprecated_params = character(),

  # arguments to get_flipped_aes that determine orientation detection
  orientation_options = list(),

  setup_params = function(self, data, params) {
    params = ggproto_parent(Stat, self)$setup_params(data, params)
    params = defaults(params, self$default_params)

    # detect orientation
    orientation_args = c(list(quote(data), quote(params)), self$orientation_options)
    params$flipped_aes = do.call(get_flipped_aes, orientation_args)
    params$orientation = get_orientation(params$flipped_aes)

    params
  },

  setup_data = function(self, data, params) {
    data = ggproto_parent(Geom, self)$setup_data(data, params)

    #set up orientation
    data$flipped_aes = params$flipped_aes

    data
  },

  # Based on ggplot2::Stat$parameters, except we always take parameters
  # from compute_panel(), because compute_group() is not used by this stat,
  # and we also take default_params instead of extra_params
  parameters = function(self, extra = TRUE) {
    panel_args = names(ggproto_formals(self$compute_panel))

    # Remove arguments of compute_group(), which are not parameters
    params = setdiff(panel_args, c(names(ggproto_formals(Stat$compute_group)), "..."))

    # we ignore the `extra` argument and just always include the "extra"
    # parameters (based on default_params instead of extra_params as in ggplot2::Stat)
    union(params, names(self$default_params))
  }
)


# make_stat ---------------------------------------------------------------

#' @importFrom rlang syms new_function pairlist2 expr
make_stat = function(stat, geom,
  mapping = NULL,
  data = NULL,
  position = "identity",
  ...
) {
  stat_name = substitute(stat)

  # stat parameters
  params = stat$default_params[!names(stat$default_params) %in% stat$hidden_params]
  params_to_defaults = lapply(params, to_expression)
  params_to_syms = syms(names(params_to_defaults))
  names(params_to_syms) = names(params_to_defaults)

  # layer arguments
  layer_function = stat$layer_function %||% "layer"
  args_to_defaults = lapply(stat$layer_args, to_expression)
  args_to_syms = syms(names(args_to_defaults))
  names(args_to_syms) = names(args_to_defaults)

  new_f = new_function(
    pairlist2(
      mapping = mapping,
      data = data,
      geom = geom,
      position = position,
      ... = ,
      !!!params_to_defaults,
      !!!args_to_defaults
    ),
    expr({                                                   # nocov start
      .Deprecated_arguments(!!stat$deprecated_params, ...)

      (!!layer_function)(
        data = data,
        mapping = mapping,
        stat = !!stat_name,
        geom = geom,
        position = position,

        !!!args_to_syms,

        params = list(
          !!!params_to_syms,
          ...
        )
      )
    }),                                                      # nocov end
    env = parent.frame()
  )
  attr(body(new_f), "srcref") = NULL

  new_f
}