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#' @title An action in a decision tree
#' @description R6 class representing an action (choice) edge.
#' @details A specialism of class \code{Arrow} which is used in a decision tree
#' to represent an edge whose source node is a \code{DecisionNode}.
#' @docType class
#' @author Andrew J. Sims \email{andrew.sims@@newcastle.ac.uk}
#' @export
#'
Action <- R6::R6Class(
classname = "Action",
lock_class = TRUE,
inherit = Arrow,
private = list(
edge_cost = NULL,
edge_benefit = NULL
),
public = list(
#' @description Create an object of type \code{Action}. Optionally, a cost
#' and a benefit may be associated with traversing the edge. A \dfn{pay-off}
#' (benefit minus cost) is sometimes used in edges of decision trees; the
#' parametrization used here is more general.
#' @param source_node Decision node from which the arrow leaves.
#' @param target_node Node to which the arrow points.
#' @param label Character string containing the arrow label. This
#' must be defined for an action because the label is used in
#' tabulation of strategies. It is recommended to choose labels that are
#' brief and not punctuated with spaces, dots or underscores.
#' @param cost Cost associated with traversal of this edge (numeric or
#' \code{ModVar}), not NA.
#' @param benefit Benefit associated with traversal of the edge, (numeric or
#' \code{ModVar}), not NA.
#' @return A new \code{Action} object.
initialize = function(source_node, target_node, label, cost = 0.0,
benefit = 0.0) {
# check label
abortifnot(
is.character(label),
nchar(label) > 0L,
message = "Argument 'label' must be a string",
class = "invalid_label"
)
# initialize base class (checks that source and target are both Nodes)
super$initialize(
source = source_node, target = target_node, label = label
)
# check that source inherits from DecisionNode
abortifnot(
inherits(source_node, what = "DecisionNode"),
message = "Node 'source_node' must be a DecisionNode",
class = "invalid_source"
)
# check and set cost, ensuring initialization
self$set_cost(cost)
# check and set benefit, ensuring initialization
self$set_benefit(benefit)
# Return Action node
return(invisible(self))
},
#' @description Find all the model variables of type \code{ModVar} that have
#' been specified as values associated with this \code{Action}. Includes
#' operands of these \code{ModVar}s, if they are expressions.
#' @return A list of \code{ModVar}s.
modvars = function() {
# create lists of input variables and output ModVars
iv <- c(private$edge_cost, private$edge_benefit)
ov <- list()
for (v in iv) {
if (is_ModVar(v)) {
ov <- c(ov, v)
if (inherits(v, what = "ExprModVar")) {
for (o in v$operands()) {
ov <- c(ov, o)
}
}
}
}
# return the unique list
return(unique(ov))
},
#' @description Return the current value of the edge probability, i.e., the
#' conditional probability of traversing the edge.
#' @return Numeric value equal to 1.
p = function() {
return(1.0)
},
#' @description Set the cost associated with the action edge.
#' @param c Cost associated with traversing the action edge. Of type numeric
#' or \code{ModVar}, not NA.
#' @return Updated \code{Action} object.
set_cost = function(c = 0.0) {
abortifnot(
inherits(c, what = c("numeric", "ModVar")),
message = "Argument 'c' must be of type 'numeric' or 'ModVar'.",
class = "invalid_cost"
)
if (inherits(c, what = "numeric")) {
abortif(
is.na(c),
message = "Setting parameter 'c' to NA is not allowed.",
class = "invalid_cost"
)
}
private$edge_cost <- c
return(invisible(self))
},
#' @description Return the cost associated with traversing the edge.
#' @return Cost.
cost = function() {
rv <- as_numeric(private$edge_cost)
return(rv)
},
#' @description Set the benefit associated with the action edge.
#' @param b Benefit associated with traversing the action edge. Of type
#' numeric or \code{ModVar}.
#' @return Updated \code{Action} object.
set_benefit = function(b = 0.0) {
abortifnot(
inherits(b, what = c("numeric", "ModVar")),
message = "Argument 'b' must be of type 'numeric' or 'ModVar'.",
class = "invalid_benefit"
)
if (inherits(b, what = "numeric")) {
abortif(
is.na(b),
message = "Setting parameter 'b' to NA is not allowed.",
class = "invalid_benefit"
)
}
private$edge_benefit <- b
return(invisible(self))
},
#' @description Return the benefit associated with traversing the edge.
#' @return Benefit.
benefit = function() {
rv <- as_numeric(private$edge_benefit)
return(rv)
}
)
)
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