map_local {tidygraph}

Map a function over a graph representing the neighborhood of each node

Description

This function extracts the neighborhood of each node as a graph and maps over each of these neighborhood graphs. Conceptually it is similar to igraph::local_scan(), but it borrows the type safe versions available in map_bfs() and map_dfs().

Usage

map_local(order = 1, mode = "all", mindist = 0, .f, ...)

map_local_lgl(order = 1, mode = "all", mindist = 0, .f, ...)

map_local_chr(order = 1, mode = "all", mindist = 0, .f, ...)

map_local_int(order = 1, mode = "all", mindist = 0, .f, ...)

map_local_dbl(order = 1, mode = "all", mindist = 0, .f, ...)

Arguments

order

Integer giving the order of the neighborhood.

mode

Character constant, it specifies how to use the direction of the edges if a directed graph is analyzed. For ‘out’ only the outgoing edges are followed, so all vertices reachable from the source vertex in at most order steps are counted. For ‘"in"’ all vertices from which the source vertex is reachable in at most order steps are counted. ‘"all"’ ignores the direction of the edges. This argument is ignored for undirected graphs.

mindist

The minimum distance to include the vertex in the result.

.f

A function to map over all nodes. See Details

...

Additional parameters to pass to .f

Details

The function provided to .f will be called with the following arguments in addition to those supplied through ...:

• neighborhood: The neighborhood graph of the node

• graph: The full tbl_graph object

• node: The index of the node currently mapped over

The neighborhood graph will contain an extra node attribute called .central_node, which will be TRUE for the node that the neighborhood is expanded from and FALSE for everything else.

Value

map_local() returns a list of the same length as the number of nodes in the graph, in the order matching the node order in the graph. ⁠map_local_*()⁠ tries to coerce its result into a vector of the classes logical (map_local_lgl), character (map_local_chr), integer (map_local_int), or double (map_local_dbl). These functions will throw an error if they are unsuccesful, so they are type safe.

Examples

# Smooth out values over a neighborhood
create_notable('meredith') %>%
  mutate(value = rpois(graph_order(), 5)) %>%
  mutate(value_smooth = map_local_dbl(order = 2, .f = function(neighborhood, ...) {
    mean(as_tibble(neighborhood, active = 'nodes')$value)
  }))