Leaflet create separate layer groups - layer

Question

I am creating a leaflet map with two different types of layers:
A layer for total rental households, and a layer for total borrowing households. This layer should be mutually exclusive: i.e., you should only be able to select one of these layers at a time (either show total rental households OR total borrowing households). This will effectively function as a base layer: you can only choose one.
A layer Sydney, and a layer for the Rest of NSW. This layer does not need to be mutually exclusive: i.e., can show both Sydney AND Rest of NSW at the same time. These will effectively function like overlays: you can choose as many as you like.
Currently, I have only figured out how to show these layers as four separate layers: Sydney Renters, Rest of NSW renters, Sydney Borrowers, Rest of NSW Borrowers. (see image)
I would like to have these as two separate layers, with a choice for Renters OR Borrowers, and a separate layer for Sydney AND/OR Rest of NSW.
Here is the code used to generate the map:
leaflet() %>%
addProviderTiles(providers$CartoDB.Positron, group = "OSM (default)") %>%
addPolygons(data = sf_syd, fillColor = ~pal2(Renting), color="white", weight=1, fillOpacity=0.4, group="Sydney Renters",
highlight = highlightOptions(weight=2, color="black", fillOpacity = 0.7, bringToFront = TRUE)) %>%
addPolygons(data = sf_nsw, fillColor = ~pal2(Renting), color="white", weight=1, fillOpacity=0.4, group="Rest of NSW Renters",
highlight = highlightOptions(weight=2, color="black", fillOpacity = 0.7, bringToFront = TRUE)) %>%
addPolygons(data = sf_syd, fillColor = ~pal2(Borrowing), color="white", weight=1, fillOpacity=0.4, group="Sydney Borrowers",
highlight = highlightOptions(weight=2, color="black", fillOpacity = 0.7, bringToFront = TRUE)) %>%
addPolygons(data = sf_nsw, fillColor = ~pal2(Borrowing), color="white", weight=1, fillOpacity=0.4, group="Rest of NSW Borrowers",
highlight = highlightOptions(weight=2, color="black", fillOpacity = 0.7, bringToFront = TRUE)) %>%
addLayersControl(baseGroups = c("OSM (default)"),
overlayGroups = c("Sydney Renters",
"Rest of NSW Renters",
"Sydney Borrowers",
"Rest of NSW Borrowers"),
options = layersControlOptions(collapsed = FALSE)) %>%
addLegend(data= sf_syd, pal = pal2, values = ~perc_rental_stress, opacity = 0.7, position = "bottomright", title = "Households of </br> Household Type 'X'")

Answer 1

What you want is a user interface to filter the data before it goes into leaflet. This is not possible in Rleaflet without a UI layer like shiny.
You can theoretically create a matrix of combinations and create a layergroup for each possibility but this will not look good when mapping.
A proper shiny based solution looks like this,
library(shiny)
library(leaflet)
library(tmap)
data(World)
ui <- fluidPage(
leafletOutput("mymap"),
p(),
br(),
checkboxInput("asia", label = "Asia", TRUE),
checkboxInput("africa", label = "Africa", TRUE),
radioButtons("value",choiceValues = c("life_exp","footprint"), choiceNames =c("life_exp","footprint"), label = "test", selected = "life_exp")
)
server <- function(input, output, session) {
filtered_world <- reactive({
temp <- World %>% filter(1==2)
if(input$asia) { temp <- rbind(temp, World %>% filter(continent == 'Asia')) }
if(input$africa) { temp <- rbind(temp, World %>% filter(continent == 'Africa')) }
temp$value <- temp[[input$value]]
temp
})
output$mymap <- renderLeaflet({
data <- filtered_world()
pal <- colorNumeric(palette = "Blues",domain = data$value)
leaflet() %>%
addProviderTiles(providers$CartoDB.PositronNoLabels) %>%
addPolygons(data = data, fillColor = ~pal(value),
fillOpacity = 1, color = "black", weight = 1)
})
}
shinyApp(ui, server)