I made the following network in R:

library(igraph)
library(reshape2)

north_american_cities <- c("New York", "Los Angeles", "Chicago", "Houston", "Phoenix")
european_cities <- c("London", "Berlin", "Madrid", "Rome", "Paris")
asian_cities <- c("Tokyo", "Delhi", "Shanghai", "Beijing", "Mumbai")

n <- 30

set.seed(123) 

na_cities_sample <- sample(north_american_cities, n, replace = TRUE)
eu_cities_sample <- sample(european_cities, n, replace = TRUE)
as_cities_sample <- sample(asian_cities, n, replace = TRUE)

df <- data.frame(NorthAmerica = na_cities_sample,
                 Europe = eu_cities_sample,
                 Asia = as_cities_sample,
                 stringsAsFactors = FALSE)

df <- df[!duplicated(df), ]

edges_df <- data.frame(from = c(df$NorthAmerica, df$Europe),
                       to = c(df$Europe, df$Asia))

edge_list <- as.matrix(edges_df)

g <- graph_from_edgelist(edge_list, directed = TRUE)
plot(g, vertex.size=10, vertex.label.cex=0.8, edge.arrow.size=0.5)

I then added a single drop down menu for navigation using visNetwork:

    library(visNetwork)
nodes_df <- data.frame(id = unique(c(df$NorthAmerica, df$Europe, df$Asia)), 
                       group = c(rep("North America", length(unique(df$NorthAmerica))),
                                 rep("Europe", length(unique(df$Europe))),
                                 rep("Asia", length(unique(df$Asia)))))

edges_df <- data.frame(from = c(df$NorthAmerica, df$Europe),
                       to = c(df$Europe, df$Asia))

colors <- c('North America' = 'red', 'Europe' = 'green', 'Asia' = 'blue')

visNetwork(nodes_df, edges_df) %>%   
    visNodes(color = list(background = colors[nodes_df$group])) %>%
    visEdges(arrows = 'to') %>%
    visOptions(highlightNearest = TRUE, nodesIdSelection = TRUE) %>%
    visInteraction(navigation = "zoom") %>%
    visInteraction(navigation = "drag")

My Question: I am trying to modify the above code to create 3 dropdown menus, that would allow someone to select a north american city and see all possible journeys that can be taken – then to click on a european city to further narrow it down:

I tried searching for examples online, but it seems like visNetwork in R might not allow this option of multiple dropdowns.

• I tried to see if there might be anything possible using javascript events
• I found some options involving R Shiny, e.g. R – state of the art performance of visNetwork vs networkd3 in a Shiny app (2017)

Can someone please show me how I might be able to add these 3 dropdowns?

Thanks!