DiagrammeR (version 0.8.2)

edge_present: Determine whether a specified edge is present in an existing graph object

Description

From a graph object of class dgr_graph, determine whether a directed edge (defined by a pair of node IDs extant in the graph) is present.

Usage

edge_present(graph, from, to)

Arguments

graph

a graph object of class dgr_graph that is created using create_graph.

from

a node ID from which the edge to be queried is outgoing.

to

a node ID to which the edge to be queried is incoming.

Value

a logical value.

Examples

## Not run: 
# # Before finding out whether a particular edge is present,
# # create a simple graph
# nodes <-
#   create_nodes(nodes = LETTERS,
#                label = TRUE,
#                type = c(rep("a_to_g", 7),
#                         rep("h_to_p", 9),
#                         rep("q_to_x", 8),
#                         rep("y_and_z",2)))
# 
# edges <-
#   create_edges(from = sample(LETTERS, replace = TRUE),
#                to = sample(LETTERS, replace = TRUE),
#                label = "edge",
#                rel = "letter_to_letter")
# 
# graph <-
#   create_graph(nodes_df = nodes,
#                edges_df = edges,
#                graph_attrs = "layout = neato",
#                node_attrs = c("fontname = Helvetica",
#                               "shape = circle"))
# 
# # Is there any edge between nodes with IDs 'A' and 'B'?
# edge_present(graph, from = "A", to = "B")
# #> FALSE
# 
# # Verify that there is an edge between nodes 'K' and 'V'
# edge_present(graph, from = "K", to = "V")
# #> TRUE
# ## End(Not run)