How to hide/toggle legends with layer controls in Leaflet for R

Question

In the package leaflet for R, you have the ability to toggle layers on and off with the addLayersControl() option. If you use legends for each individual layer, however, these layers are not toggled on and off with the layers control. Here's a quick reproducible example of what I'm working with:

library(raster)
library(leaflet)

#load in shapefiles, trim excess data
gtm <- getData('GADM', country = 'GTM', level = 0)
gtm <- gtm[, -c(2:68)]

mex <- getData('GADM', country = 'MEX', level = 0)
mex <- mex[, -c(2:68)]


leaflet() %>%
  addTiles() %>% 
  addPolygons(data = gtm, 
              fillColor = 'red', 
              group = "gtm") %>% 
  addLegend(color = "red",
            labels = gtm@data$OBJECTID) %>% 
  addPolygons(data = mex, 
              fillColor = 'blue', 
              group = "mex") %>% 
  addLegend(color = "blue", 
            labels = mex@data$OBJECTID) %>% 
  addLayersControl(overlayGroups = c("gtm", "mex"), 
                   options = layersControlOptions(collapsed = F))][1]][1]

As you can see above, when I toggle the Mexico layer off, its legend remains. I've searched the question a bit, but all of the questions appear to be applicable to Leaflet.js rather than the R package. Is there any way to control the legends in Leaflet for R so that they can also toggle on and off?

Answer 1

You can add legend to the same group, then it will show/hide legend and polygons both. Learn more here.

library(raster)
library(leaflet)

#load in shapefiles
gtm <- getData('GADM', country = 'GTM', level = 0)
mex <- getData('GADM', country = 'MEX', level = 0)

leaflet() %>%
  addTiles() %>% 
  addPolygons(data = gtm, 
              fillColor = 'red', 
              group = "gtm") %>% 
  addLegend(color = "red",
            labels = gtm@data$GID_0, 
            group = "gtm") %>% 

  addPolygons(data = mex, 
              fillColor = 'blue', 
              group = "mex") %>% 
  addLegend(color = "blue", 
        labels = mex@data$GID_0,
        group = "mex") %>% 

  addLayersControl(overlayGroups = c("gtm", "mex"), 
               options = layersControlOptions(collapsed = F))

Answer 2

We solved this by controlling layer visibility with a shiny switch input and manually clearing the group and removing the legend:

map %>% clearGroup("zones") %>% removeControl("zonesLegend")

If you're not using shiny you can add some custom JS with htmlwidgets::onRender that listens for changes to the layer control and removes the appropriate controls.