R/sbn_down_dir.R

In SBN: Generate Stochastic Branching Networks

#' Convert to a downstream directed network
#'
#' Convert an upstream directed or non-directed network to a downstream directed network.
#'
#' @param g a river network as an igraph object.
#'
#' @param mouth river mouth vertex id.
#'
#' @return A downstream directed network.
#'
#' @importFrom igraph as.directed as.undirected V ends E as_ids shortest_paths graph_from_edgelist
#'
#' @examples
#' g <- sbn_create(10, 0.7)
#'
#' # to undirected
#' g <- sbn_change_dir(g, method = "undir")
#'
#' # undirected to downstream directed
#' sbn_down_dir(g, mouth = 1)
#'
#' @export
sbn_down_dir <- function(g, mouth){

  g2 <- igraph::as.directed(igraph::as.undirected(g), mode = "mutual")

  x <- igraph::shortest_paths(graph = g2, from = mouth,
                              to = igraph::V(g2),
                              output = "epath", mode = "in")[2][[1]]

  y <- igraph::ends(g2, igraph::E(g2))
  y <- y[unique(unlist(lapply(x, igraph::as_ids))), ]
  g <- igraph::graph_from_edgelist(y)
  return(g)
}