trav_out {DiagrammeR}

Traverse from one or more selected nodes onto adjacent, outward nodes

Description

From a graph object of class dgr_graph move along outward edges from one or more nodes present in a selection to other connected nodes, replacing the current nodes in the selection with those nodes traversed to. An optional filter by node attribute can limit the set of nodes traversed to.

This traversal function makes use of an active selection of nodes. After the traversal, depending on the traversal conditions, there will either be a selection of nodes or no selection at all.

Selections of nodes can be performed using the following node selection (⁠select_*()⁠) functions: select_nodes(), select_last_nodes_created(), select_nodes_by_degree(), select_nodes_by_id(), or select_nodes_in_neighborhood().

Selections of nodes can also be performed using the following traversal (⁠trav_*()⁠) functions: trav_out(), trav_in(), trav_both(), trav_out_node(), trav_in_node(), trav_out_until(), or trav_in_until().

Usage

trav_out(
  graph,
  conditions = NULL,
  copy_attrs_from = NULL,
  copy_attrs_as = NULL,
  agg = "sum",
  add_to_selection = FALSE
)

Arguments

graph

A graph object of class dgr_graph.

conditions

An option to use filtering conditions for the traversal.

copy_attrs_from

Providing a node attribute name will copy those node attribute values to the traversed nodes. Any values extant on the nodes traversed to will be replaced.

copy_attrs_as

If a node attribute name is provided in copy_attrs_from, this option will allow the copied attribute values to be written under a different attribute name. If the attribute name provided in copy_attrs_as does not exist in the graph's ndf, the new node attribute will be created with the chosen name.

agg

If a node attribute is provided to copy_attrs_from, then an aggregation function is required since there may be cases where multiple edge attribute values will be passed onto the traversed node(s). To pass only a single value, the following aggregation functions can be used: sum, min, max, mean, or median.

add_to_selection

An option to either add the traversed to nodes to the active selection of nodes (TRUE) or switch the active selection entirely to those traversed to nodes (FALSE, the default case).

Value

A graph object of class dgr_graph.

Examples

# Set a seed
suppressWarnings(RNGversion("3.5.0"))
set.seed(23)

# Create a simple graph
graph <-
  create_graph() %>%
  add_n_nodes(
    n = 2,
    type = "a",
    label = c("asd", "iekd")) %>%
  add_n_nodes(
    n = 3,
    type = "b",
    label = c("idj", "edl", "ohd")) %>%
  add_edges_w_string(
    edges = "1->2 1->3 2->4 2->5 3->5",
    rel = c(NA, "A", "B", "C", "D"))

# Create a data frame with node ID values
# representing the graph edges (with `from`
# and `to` columns), and, a set of numeric values
df_edges <-
  data.frame(
    from = c(1, 1, 2, 2, 3),
    to = c(2, 3, 4, 5, 5),
    values = round(rnorm(5, 5), 2))

# Create a data frame with node ID values
# representing the graph nodes (with the `id`
# columns), and, a set of numeric values
df_nodes <-
  data.frame(
    id = 1:5,
    values = round(rnorm(5, 7), 2))

# Join the data frame to the graph's internal
# edge data frame (edf)
graph <-
  graph %>%
  join_edge_attrs(df = df_edges) %>%
  join_node_attrs(df = df_nodes)

# Show the graph's internal node data frame
graph %>% get_node_df()

# Show the graph's internal edge data frame
graph %>% get_edge_df()

# Perform a simple traversal from node `3`
# to outward adjacent nodes with no conditions
# on the nodes traversed to
graph %>%
  select_nodes_by_id(nodes = 3) %>%
  trav_out() %>%
  get_selection()

# Traverse from node `1` to outbound
# nodes, filtering to those nodes that have
# numeric values greater than `7.0` for
# the `values` node attribute
graph %>%
  select_nodes_by_id(nodes = 1) %>%
  trav_out(
    conditions = values > 7.0) %>%
  get_selection()

# Traverse from node `1` to any outbound
# nodes, filtering to those nodes that
# have a `type` attribute of `b`
graph %>%
  select_nodes_by_id(nodes = 1) %>%
  trav_out(
    conditions = type == "b") %>%
  get_selection()

# Traverse from node `2` to any outbound
# nodes, filtering to those nodes that
# have a degree of `1`
graph %>%
  {
  node_degrees <-
    get_node_info(.) %>%
    dplyr::select(id, deg)
  join_node_attrs(
    graph = .,
    df = node_degrees)
  } %>%
  select_nodes_by_id(nodes = 2) %>%
  trav_out(
    conditions = deg == 1) %>%
  get_selection()

# Traverse from node `2` to any outbound
# nodes, and use multiple conditions for
# the traversal
graph %>%
  select_nodes_by_id(nodes = 2) %>%
  trav_out(
    conditions =
      type == "a" &
      values > 8.0) %>%
  get_selection()

# Traverse from node `2` to any
# outbound nodes, and use multiple
# conditions with a single-length vector
graph %>%
  select_nodes_by_id(nodes = 2) %>%
  trav_out(
    conditions =
      type == "b" |
      values > 8.0) %>%
  get_selection()

# Traverse from node `2` to any outbound
# nodes, and use a regular expression as
# a filtering condition
graph %>%
  select_nodes_by_id(nodes = 2) %>%
  trav_out(
    conditions = grepl("..d", label)) %>%
  get_selection()

# Create another simple graph to demonstrate
# copying of node attribute values to traversed
# nodes
graph <-
  create_graph() %>%
  add_node() %>%
  select_nodes() %>%
  add_n_nodes_ws(
    n = 2,
    direction = "to") %>%
  clear_selection() %>%
  select_nodes_by_id(nodes = 2:3) %>%
  set_node_attrs_ws(
    node_attr = value,
    value = 5)

# Show the graph's internal node data frame
graph %>% get_node_df()

# Show the graph's internal edge data frame
graph %>% get_edge_df()

# Perform a traversal from the outer nodes
# (`2` and `3`) to the central node (`1`) while
# also applying the node attribute `value` to
# node `1` (summing the `value` of 5 from
# both nodes before applying that value to the
# target node)
graph <-
  graph %>%
  trav_out(
    copy_attrs_from = value,
    agg = "sum")

# Show the graph's internal node data
# frame after this change
graph %>% get_node_df()