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.
@helgasoft, thank you for sharing your code! Do you know the 'hook-up' object syntaxes for polygons, polylines or markers?
My attempt to integrate the leaflet-groupedlayercontrol plugin have so far been unsuccessful. Thanks in advance for any tips you might offer.