targets.R

#' @include internal.R pproto.R ProjectProblem-proto.R
NULL

#' Targets
#'
#' Targets are used to specify the minimum probability of persistence required
#' for each feature. Please note that only some objectives require
#' targets, and attempting to solve a problem that requires targets will throw
#' an error if targets are not supplied, and attempting to solve a problem that
#' does not require targets will throw a warning if targets are supplied.
#'
#' @details The following functions can be used to specify targets for a
#'   project prioritization [problem()]:
#'
#'   \describe{
#'
#'   \item{[add_relative_targets()]}{
#'     Set targets as a proportion (between 0 and 1) of the maximum probability
#'     of persistence associated with the best project for each feature. For
#'     instance, if the best project for a feature has an 80% probability of
#'     persisting, setting a 50% (i.e. `0.5`) relative target will
#'     correspond to a 40% threshold probability of persisting.}
#'
#'   \item{[add_absolute_targets()]}{
#'     Set targets by specifying exactly what probability of persistence is
#'     required for each feature. For instance, setting an absolute target of
#'     10% (i.e. `0.1`) corresponds to a threshold 10% probability of
#'     persisting.}
#'
#'   \item{[add_manual_targets()]}{
#'     Set targets by manually specifying all the required information for each
#'     target.}
#'
#'   }
#'
#' @seealso [constraints], [decisions],
#'  [objectives], [problem()],
#'  [solvers].
#'
#' @examples
#' # load data
#' data(sim_projects, sim_features, sim_actions)
#'
#' # build problem with minimum set objective and targets that require each
#' # feature to have a 30% chance of persisting into the future
#' p1 <- problem(sim_projects, sim_actions, sim_features,
#'              "name", "success", "name", "cost", "name") %>%
#'       add_min_set_objective() %>%
#'       add_absolute_targets(0.3) %>%
#'       add_binary_decisions()
#'
#' # print problem
#' print(p1)
#'
#' # build problem with minimum set objective and targets that require each
#' # feature to have a level of persistence that is greater than or equal to
#' # 30% of the best project for conserving it
#' p2 <- problem(sim_projects, sim_actions, sim_features,
#'              "name", "success", "name", "cost", "name") %>%
#'       add_min_set_objective() %>%
#'       add_relative_targets(0.3) %>%
#'       add_binary_decisions()
#'
#' # print problem
#' print(p2)
#'
#' \dontrun{
#' # solve problems
#' s1 <- solve(p1)
#' s2 <- solve(p2)
#'
#' # print solutions
#' print(s1)
#' print(s2)
#'
#' # plot solutions
#' plot(p1, s1)
#' plot(p2, s2)
#' }
#' @name targets
NULL

add_default_targets <- function(x) {
  # assert arguments are valid
  assertthat::assert_that(inherits(x, "ProjectProblem"))
  # throw error because targets must be chosen by the user
  stop("problem is missing targets and they must be explicitly defined")
}