This is a very simple function to perform geocoding using the Google Maps API:

getGeoCode <- function(gcStr, key)  {
  library("RJSONIO") #Load Library
  gcStr <- gsub(' ','%20',gcStr) #Encode URL Parameters
  #Open Connection
  connectStr <- paste0('https://maps.googleapis.com/maps/api/geocode/json?address=',gcStr, "&key=",key) 
  con <- url(connectStr)
  data.json <- fromJSON(paste(readLines(con), collapse=""))
  close(con)
  #Flatten the received JSON
  data.json <- unlist(data.json)
  if(data.json["status"]=="OK")   {
    lat <- data.json["results.geometry.location.lat"]
    lng <- data.json["results.geometry.location.lng"]
    gcodes <- c(lat, lng)
    names(gcodes) <- c("Lat", "Lng")
    return (gcodes)
  }
}

Essentially, users need to get an API key from google and then use as an input (string) for the function. The function itself is very simple, and it is an adaptation of some code I found on-line (unfortunately I did not write down where I found the original version so I do not have a way to reference the source, sorry!!).

geoCodes <- getGeoCode(gcStr="11 via del piano, empoli", key)

To use the function we simply need to include an address, and it will return its coordinates in WGS84.
It can be used in a mutate call within dplyr and it is reasonably fast.

The repository is here:
https://github.com/fveronesi/RGeocode.r