Merge directed edges into equivalent undirected edges.

Merge directed edges into equivalent undirected values by aggregating across directions. This function is primarily intended to aid visualisation of directed graphs, particularly visualising the results of the dodgr_flows_aggregate and dodgr_flows_disperse functions, which return columns of aggregated flows directed along each edge of a graph.

Usage

merge_directed_graph(graph, col_names = c("flow"))

Arguments

graph

A undirected graph in which directed edges of the input graph have been merged through aggregation to yield a single, undirected edge between each pair of vertices.

col_names

Names of columns to be merged through aggregation. Values for these columns in resultant undirected graph will be aggregated from directed values.

Value

An equivalent graph in which all directed edges have been reduced to single, undirected edges, and all values of the specified column(s) have been aggregated across directions to undirected values.

See also

Other misc: compare_heaps(), dodgr_flowmap(), dodgr_full_cycles(), dodgr_fundamental_cycles(), dodgr_insert_vertex(), dodgr_sample(), dodgr_sflines_to_poly(), dodgr_vertices(), summary.dodgr_dists_categorical(), write_dodgr_wt_profile()

Examples

graph <- weight_streetnet (hampi)
from <- sample (graph$from_id, size = 10)
to <- sample (graph$to_id, size = 5)
to <- to [!to %in% from]
flows <- matrix (10 * runif (length (from) * length (to)),
    nrow = length (from)
)
graph <- dodgr_flows_aggregate (graph, from = from, to = to, flows = flows)
# graph then has an additonal 'flows` column of aggregate flows along all
# edges. These flows are directed, and can be aggregated to equivalent
# undirected flows on an equivalent undirected graph with:
graph_undir <- merge_directed_graph (graph)
# This graph will only include those edges having non-zero flows, and so:
nrow (graph)
#> [1] 6813
nrow (graph_undir) # the latter is much smaller
#> [1] 1053