The dodgr_flows_aggregate and dodgr_flows_disperse functions return a column of aggregated flows directed along each edge of a graph, so the aggregated flow from vertex A to vertex B will not necessarily equal that from B to A, and the total flow in both directions will be the sum of flow from A to B plus that from B to A. This function converts a directed graph to undirected form through reducing all pairs of directed edges to a single edge, and aggregating flows from both directions.




A graph containing a flow column as returned from dodgr_flows_aggregate or dodgr_flows_disperse


An equivalent graph in which all directed edges have been reduced to single, undirected edges, and all directed flows aggregated to undirected flows.


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_flows (graph) # This graph will only include those edges having non-zero flows, and so: nrow (graph); nrow (graph_undir) # the latter is much smaller
#> [1] 5973
#> [1] 1067