How to use Igraph with leaflet for R?

Question

I try to draw a graph in map with R

code :

df<-data.frame("from" = c("Lyon", "Toulouse", "Paris", "Marseille"), 
               "to"= c("Paris", "Paris", "Marseille", "Toulouse"))
meta <- data.frame("name"=c("Lyon", "Toulouse", "Paris", "Marseille"), 
                   "lon"=c(-4.850000, 1.444209, 2.352222, 5.36978),  
                   "lat"=c(45.750000, 43.604652, 48.856614, 43.296482))

g <- graph.data.frame(df, directed=FALSE, vertices=meta)
lo <- layout.norm(as.matrix(meta[,2:3]))
plot.igraph(g, layout=lo,vertex.size = 60,
            vertex.color="red",
            vertex.frame.color= "white",
            vertex.label.color = "white",
            vertex.label.family = "sans",
            edge.width=2,  
            edge.color="black")

but I do not find a way that allows me to display it on the map using leaflet, someone has an idea please?

Answer 1

Here is one possible way, by first converting your graph to spatial object and using plotting these with with the leaflet package.

library(sp)
gg <- get.data.frame(g, "both")
vert <- gg$vertices
coordinates(vert) <- ~lon+lat

edges <- gg$edges

edges <- lapply(1:nrow(edges), function(i) {
  as(rbind(vert[vert$name == edges[i, "from"], ], 
           vert[vert$name == edges[i, "to"], ]), 
     "SpatialLines")
})


for (i in seq_along(edges)) {
  edges[[i]] <- spChFIDs(edges[[i]], as.character(i))
}

edges <- do.call(rbind, edges)


library(leaflet)
leaflet(vert) %>% addTiles() %>% addMarkers(data = vert) %>% addPolylines(data = edges)

You may want to improve the styling.