Extract Nodes from Graph — nodes_from

Extract unique nodes with their coordinates from a graph data frame.

Usage

nodes_from_graph(graph_df, sf = FALSE, crs = 4326)

Arguments

graph_df: A data frame representing a graph with columns: from, to, FX, FY, TX, TY.
sf: Logical. If TRUE, returns result as an sf POINT object. Default: FALSE.
crs: Coordinate reference system for sf output; default is 4326.

Value

A data frame (or sf object if sf = TRUE) with unique nodes and coordinates:

node - Node ID
X - Node X-coordinate (typically longitude)
Y - Node Y-coordinate (typically latitude)

Result is sorted by node ID.

Details

This function extracts all unique nodes from both the from and to columns of the graph, along with their corresponding coordinates. Duplicate nodes are removed, keeping only unique node IDs with their coordinates.

Examples

library(flownet)
library(sf)

# Load existing network edges and convert to graph
africa_net <- africa_network[!africa_network$add, ]
graph <- linestrings_to_graph(africa_net)

# Extract nodes from graph
nodes <- nodes_from_graph(graph)
head(nodes)
#>   node         X        Y
#> 1    1 -17.44671 14.69281
#> 2    2 -17.04453 14.70297
#> 3    3 -16.63849 15.11222
#> 4    4 -16.46332 14.75651
#> 5    5 -16.42054 14.34236
#> 6    6 -17.03333 20.93330

# Get nodes as sf POINT object for spatial operations
nodes_sf <- nodes_from_graph(graph, sf = TRUE)
class(nodes_sf)
#> [1] "sf"         "data.frame"

# Find nearest network nodes to cities/ports
nearest_nodes <- nodes_sf$node[st_nearest_feature(africa_cities_ports, nodes_sf)]
head(nearest_nodes)
#> [1]  903  275  609  553  880 1372