Using arbitrary Leaflet plugins with Leaflet for R

README.md

Using arbitrary Leaflet JS plugins with Leaflet for R

The Leaflet JS mapping library has lots of plugins available. The Leaflet package for R provides direct support for some, but far from all, of these plugins, by providing R functions for invoking the plugins.

If you as an R user find yourself wanting to use a Leaflet plugin that isn't directly supported in the R package, you can use the technique shown here to load the plugin yourself and invoke it using JS code.

leaflet-esri.R

library(leaflet)
library(htmltools)
library(htmlwidgets)

# This tells htmlwidgets about our plugin name, version, and
# where to find the script. (There's also a stylesheet argument
# if the plugin comes with CSS files.)
esriPlugin <- htmlDependency("leaflet.esri", "1.0.3",
  src = c(href = "https://cdn.jsdelivr.net/leaflet.esri/1.0.3/"),
  script = "esri-leaflet.js"
)

# A function that takes a plugin htmlDependency object and adds
# it to the map. This ensures that however or whenever the map
# gets rendered, the plugin will be loaded into the browser.
registerPlugin <- function(map, plugin) {
  map$dependencies <- c(map$dependencies, list(plugin))
  map
}


leaflet() %>% setView(-122.23, 37.75, zoom = 10) %>%
  # Register ESRI plugin on this map instance
  registerPlugin(esriPlugin) %>%
  # Add your custom JS logic here. The `this` keyword
  # refers to the Leaflet (JS) map object.
  onRender("function(el, x) {
    L.esri.basemapLayer('Topographic').addTo(this);
  }")

leaflet-heat.R

# This example shows the ability to pass extra R data to onRender.
# At the time of this writing it requires a custom build of htmlwidgets:
# devtools::install_github("ramnathv/htmlwidgets@joe/feature/onrender-data")
#
# Track the progress of this functionality at
# https://github.com/ramnathv/htmlwidgets/pull/202

library(leaflet)
library(htmltools)
library(htmlwidgets)
library(dplyr)

heatPlugin <- htmlDependency("Leaflet.heat", "99.99.99",
  src = c(href = "http://leaflet.github.io/Leaflet.heat/dist/"),
  script = "leaflet-heat.js"
)

registerPlugin <- function(map, plugin) {
  map$dependencies <- c(map$dependencies, list(plugin))
  map
}

leaflet() %>% addTiles() %>%
  fitBounds(min(quakes$long), min(quakes$lat), max(quakes$long), max(quakes$lat)) %>%
  registerPlugin(heatPlugin) %>%
  onRender("function(el, x, data) {
    data = HTMLWidgets.dataframeToD3(data);
    data = data.map(function(val) { return [val.lat, val.long, val.mag*100]; });
    L.heatLayer(data, {radius: 25}).addTo(this);
  }", data = quakes %>% select(lat, long, mag))

Very helpful. But I've struggled to figure out how I can extend this logic to enable the display of a Google Maps baselayers (via Pavel Shramov's Google plugin for Leaflet). If you could add another gist showing this, I'd be much obliged. Thanks!