R/add_forward_edges_ws.R

In DiagrammeR: Graph/Network Visualization

#' Add new edges with identical definitions as with a selection of edges
#'
#' @description
#'
#' Add edges in the same direction of one or more edges available as an edge
#' selection in a graph object of class `dgr_graph`. New graph edges have the
#' same edge definitions as those in the selection except with new edge ID
#' values. There is also the option to assign a common `rel` grouping to the
#' newly created edges. Upon addition of the edges, the edge selection will be
#' retained for further selection or traversal operations.
#'
#' This function makes use of an active selection of edges (and the function
#' ending with `_ws` hints at this).
#'
#' Selections of edges can be performed using the following selection
#' (`select_*()`) functions: [select_edges()], [select_last_edges_created()],
#' [select_edges_by_edge_id()], or [select_edges_by_node_id()].
#'
#' Selections of edges can also be performed using the following traversal
#' (`trav_*()`) functions: [trav_out_edge()], [trav_in_edge()],
#' [trav_both_edge()], or [trav_reverse_edge()].
#'
#' @inheritParams render_graph
#' @param rel An optional string to apply a `rel` attribute to all newly created
#'   edges.
#'
#' @return A graph object of class `dgr_graph`.
#'
#' @examples
#' # Create an empty graph, add 2 nodes
#' # to it, and create the edge `1->2`
#' graph <-
#'   create_graph() %>%
#'   add_n_nodes(
#'     n = 2,
#'     type = "type_a",
#'     label = c("a_1", "a_2")) %>%
#'   add_edge(
#'     from = 1, to = 2, rel = "a")
#'
#' # Get the graph's edges
#' graph %>% get_edge_ids()
#'
#' # Select the edge and create 2
#' # additional edges with the same
#' # definition (`1->2`) but with
#' # different `rel` values (`b` and `c`)
#' graph <-
#'   graph %>%
#'   select_edges() %>%
#'   add_forward_edges_ws(rel = "b") %>%
#'   add_forward_edges_ws(rel = "c") %>%
#'   clear_selection()
#'
#' # Get the graph's edge data frame
#' graph %>% get_edge_df()
#'
#' @family Edge creation and removal
#'
#' @export
add_forward_edges_ws <- function(
    graph,
    rel = NULL
) {

  # Get the time of function start
  time_function_start <- Sys.time()

  # Get the name of the function
  fcn_name <- get_calling_fcn()

  # Validation: Graph object is valid
  if (graph_object_valid(graph) == FALSE) {

    emit_error(
      fcn_name = fcn_name,
      reasons = "The graph object is not valid")
  }

  # Validation: Graph contains edges
  if (graph_contains_edges(graph) == FALSE) {

    emit_error(
      fcn_name = fcn_name,
      reasons = "The graph contains no edges")
  }

  # Validation: Graph object has valid edge selection
  if (graph_contains_edge_selection(graph) == FALSE) {

    emit_error(
      fcn_name = fcn_name,
      reasons = "The graph contains no selection of edges")
  }

  # If no value(s) provided for `rel`, set to NA
  if (is.null(rel)) {
    rel <- as.character(NA)
  }

  # Get a vector of edges available in the
  # graph's selection
  edges_in_selection <-
    graph$edge_selection %>%
    dplyr::select(from, to)

  # Get the number of edges in the graph
  edges_graph_1 <- graph %>% count_edges()

  # Add new edges to the graph for every edge
  # in the graph's active selection
  for (i in 1:nrow(edges_in_selection)) {

    # Create a graph edge
    graph <-
      add_edge(
        graph = graph,
        from = edges_in_selection[i, 1],
        to = edges_in_selection[i, 2],
        rel = rel)

    # Redact the signing of the action to the log
    graph$graph_log <-
      graph$graph_log[-nrow(graph$graph_log), ]
  }

  # Get the updated number of edges in the graph
  edges_graph_2 <- graph %>% count_edges()

  # Get the number of edges added to
  # the graph
  edges_added <- edges_graph_2 - edges_graph_1

  # Update the `graph_log` df with an action
  graph$graph_log <-
    add_action_to_log(
      graph_log = graph$graph_log,
      version_id = nrow(graph$graph_log) + 1,
      function_used = fcn_name,
      time_modified = time_function_start,
      duration = graph_function_duration(time_function_start),
      nodes = nrow(graph$nodes_df),
      edges = nrow(graph$edges_df),
      d_e = edges_added)

  # Perform graph actions, if any are available
  if (nrow(graph$graph_actions) > 0) {
    graph <-
      graph %>%
      trigger_graph_actions()
  }

  # Write graph backup if the option is set
  if (graph$graph_info$write_backups) {
    save_graph_as_rds(graph = graph)
  }

  graph
}