R/convert_edges.R

In edgebundle: Algorithms for Bundling Edges in Networks and Visualizing Flow and Metro Maps

#' @title Convert edges
#' @description converts edges of an igraph/network/tidygraph object into format useable for edge bundling
#' @param object graph object
#' @param coords coordinates of vertices
#' @return data frame of edges with coordinates
#' @author David Schoch
#' @export
#'
convert_edges <- function(object, coords) UseMethod("convert_edges")

#' @rdname convert_edges
#' @method convert_edges default
#' @export
convert_edges.default <- function(object, coords) {
    stop("don't know how to handle class ", dQuote(data.class(object)))
}

#' @rdname convert_edges
#' @method convert_edges igraph
#' @export
convert_edges.igraph <- function(object, coords) {
    if (!requireNamespace("igraph", quietly = TRUE)) {
        stop("The `igraph` package is required for this functionality")
    }
    el <- igraph::as_edgelist(object, names = FALSE)
    if (igraph::vcount(object) != nrow(coords)) {
        stop("number of rows in `coords` does not match number of vertices")
    }
    edges_xy <- cbind(coords[el[, 1], 1], coords[el[, 1], 2], coords[el[, 2], 1], coords[el[, 2], 2])
    edges_xy
}

#' @rdname convert_edges
#' @method convert_edges network
#' @export
convert_edges.network <- function(object, coords) {
    if (!requireNamespace("network", quietly = TRUE)) {
        stop("The `network` package is required for this functionality")
    }
    el <- network::as.edgelist(object)
    if (network::get.network.attribute(object, "n") != nrow(coords)) {
        stop("number of rows in `coords` does not match number of vertices")
    }
    edges_xy <- cbind(coords[el[, 1], 1], coords[el[, 1], 2], coords[el[, 2], 1], coords[el[, 2], 2])
    edges_xy
}


#' @rdname convert_edges
#' @method convert_edges tbl_graph
#' @export
convert_edges.tbl_graph <- function(object, coords) {
    if (!requireNamespace("tidygraph", quietly = TRUE)) {
        stop("The `tidygraph` package is required for this functionality")
    }
    el <- as.matrix(tidygraph::as_tibble(object, "edges"))
    edges_xy <- cbind(coords[el[, 1], 1], coords[el[, 1], 2], coords[el[, 2], 1], coords[el[, 2], 2])
    edges_xy
}