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# IGraph R package
# Copyright (C) 2005-2012 Gabor Csardi <csardi.gabor@gmail.com>
# 334 Harvard street, Cambridge, MA 02139 USA
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
# 02110-1301 USA
#
###################################################################
#' Is this object an igraph graph?
#'
#' @aliases is.igraph
#' @param graph An R object.
#' @return A logical constant, \code{TRUE} if argument \code{graph} is a graph
#' object.
#' @author Gabor Csardi \email{csardi.gabor@@gmail.com}
#' @export
#' @keywords graphs
#' @examples
#'
#' g <- make_ring(10)
#' is_igraph(g)
#' is_igraph(numeric(10))
is_igraph <- function(graph){
"igraph" %in% class(graph)
}
#' @export
get.edge <- function(graph, id) {
.Deprecated("ends", msg = paste("'get.edge' is deperecated, please use",
"'ends' instead."))
if (!is_igraph(graph)) {
stop("Not a graph object")
}
id <- as.numeric(id)
ec <- ecount(graph)
if (id < 1 || id > ec) {
stop("No such edge")
}
on.exit( .Call("R_igraph_finalizer", PACKAGE="igraph") )
res <- .Call("R_igraph_get_edge", graph, as.numeric(id)-1,
PACKAGE="igraph")
res+1
}
#' Head of the edge(s) in a graph
#'
#' For undirected graphs, head and tail is not defined. In this case
#' \code{head_of} returns vertices incident to the supplied edges, and
#' \code{tail_of} returns the other end(s) of the edge(s).
#'
#' @param graph The input graph.
#' @param es The edges to query.
#' @return A vertex sequence with the head(s) of the edge(s).
#'
#' @family structural queries
#'
#' @export
head_of <- function(graph, es) {
create_vs(graph, ends(graph, es, names = FALSE)[,1])
}
#' Tails of the edge(s) in a graph
#'
#' For undirected graphs, head and tail is not defined. In this case
#' \code{tail_of} returns vertices incident to the supplied edges, and
#' \code{head_of} returns the other end(s) of the edge(s).
#'
#' @param graph The input graph.
#' @param es The edges to query.
#' @return A vertex sequence with the tail(s) of the edge(s).
#'
#' @family structural queries
#'
#' @export
tail_of <- function(graph, es) {
create_vs(graph, ends(graph, es, names = FALSE)[,2])
}
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