From a graph object of class dgr_graph, determine whether an edge (defined by a pair of node IDs or node label values) is present.

## Usage

is_edge_present(graph, edge = NULL, from = NULL, to = NULL)

## Arguments

graph

A graph object of class dgr_graph.

edge

An edge ID value to test for presence in the graph. If a single, numeric value is provided then values for from or to needn't be supplied.

from

A node ID from which the edge is outgoing, or, the label associated with the node. For an undirected graph, the value in from can be interchangeable with that in to.

to

A node ID to which the edge is incoming, or, the label associated with the node. For an undirected graph, the value in to can be interchangeable with that in from.

A logical value.

## Examples

# Create a simple graph with
# a path of four nodes
graph <-
create_graph() %>%
n = 4,
type = "path",
label = c("one", "two",
"three", "four"))

# Find out if edge ID 3
# is present in the graph
graph %>%
is_edge_present(edge = 3)
#> [1] TRUE

# Determine if there are any edges
# with the definition 1 -> 2
graph %>%
is_edge_present(
from = 1,
to = 2)
#> [1] TRUE

# Determine if there are any edges
# with the definition 4 -> 5
graph %>%
is_edge_present(
from = 4,
to = 5)
#> [1] FALSE

# Determine whether an edge,
# defined by its labels as
# two -> three, exists in
# the graph
graph %>%
is_edge_present(
from = "two",
to = "three")
#> [1] TRUE

# Set the graph as undirected
# and determine whether an
# edge between nodes with labels
# three and two exists
graph %>%
set_graph_undirected() %>%
is_edge_present(
from = "three",
to = "two")
#> [1] TRUE