DiagrammeR (version 0.8.4)

edge_rel: Create, read, update, delete, or report status of an edge relationship

Description

From a graph object of class dgr_graph, query an edge in the graph (defined by a pair of node IDs extant in the graph) and perform operations on the relationship for that edge.

Usage

edge_rel(graph, from, to, action = "read", value = NULL)

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.

action

the operation to perform on the edge's relationship attribute. To remove a relationship from an edge, use either delete, remove, or drop. To add a relationship to an edge with no set relationship, use add or create. To update an edge relationship, use update. To return the value of an edge relationship, use read. To determine whether there is a set relationship, use check.

value

a string denoting the relationship, to be supplied when either adding or updating an edge relationship.

Value

a graph object of class dgr_graph.

Examples

library(magrittr)

# Create a node data frame (ndf)
nodes <-
  create_nodes(
    nodes = 1:5,
    type = c("a", "b", "c", "a", "c"))

# Create an edge data frame (edf)
edges <-
  create_edges(
    from = c(1, 3, 5, 2, 4),
    to = c(2, 2, 4, 4, 3),
    rel = c("rel_a", "rel_b",
            "rel_b", "rel_a",
            "rel_c"))

# Create a graph
graph <-
  create_graph(nodes_df = nodes,
               edges_df = edges)

# Read the edge `rel` for edge `1` -> `2`
graph %>%
  edge_rel(1, 2)
#> [1] "rel_a"

# Remove the `rel` value entirely from
# edge `1` -> `2`
graph %<>%
  edge_rel(1, 2, "delete")

# Check that the edge `1` -> `2` no longer
# has a `rel` assignment
graph %>%
  edge_rel(1, 2, "check")
#> [1] FALSE

# Add the `rel` value `rel_b`` to edge `1` -> `2`
graph %<>%
  edge_rel(1, 2, "add", "rel_b")

# Read the edge `rel` for edge `1` -> `2`
graph %>%
  edge_rel(1, 2)
#> [1] "rel_b"

# Perform an in-place update of the `rel`
# value for edge `1` -> `2` (`rel_b`` to `rel_a``)
graph %<>%
  edge_rel(1, 2, "update", "rel_a")

# Read the edge `rel` for edge `1` -> `2`
# to ensure that the change was made
graph %>%
  edge_rel(1, 2)
#> [1] "rel a"