Shiny leaflet display point weight based on zoom level breaks down when using if-else statement

Question

I have a basic shiny app with a leaflet map.The circles should stay as they are until a user zooms to zoom-level 8, at which point the weight should be 2. When the zoom becomes 9 or higher, the weight should become 3.

Here is my attempt. The app breaks down when I go to zoom level 9 with Error in resolveFormula: Unexpected two-sided formula: (input$map_zoom > 8) ~ 3

## app.R ##
library(leaflet)
library(shinydashboard)
library(shinydashboardPlus)

ui <- dashboardPage(
  dashboardHeader(title = "Basic dashboard"),
  dashboardSidebar(),
  dashboardBody(
    leafletOutput("map", width = "100%", height = "500px")
    
  )
)

server <- function(input, output,session) {
  
  df <- data.frame("Lat"=c(32.921821,32.910853,32.793803,32.995084,32.683745,32.759999,32.800652,32.958861,32.835963,32.762578,32.649651,32.862843,32.862217,32.936876,32.963381),
                   "Long"=c(-96.840609,-96.738831,-96.689232,-96.857858,-96.825345,-96.684475,-96.794144,-96.816111,-96.676371,-96.897331,-96.944426,-96.754719,-96.856976,-96.752718,-96.770249))
  
  observeEvent(
    eventExpr = input$map_zoom, {
      print(input$map_zoom)           # Display zoom level in the console
      leafletProxy(
        mapId = "map", 
        session = session
      )%>% 
        addCircles(data=df,lng = ~Long, lat = ~Lat, weight = if(input$map_zoom <=8) ~2
                   else(input$map_zoom >8) ~3,
                   opacity = 1, fill = TRUE, fillOpacity = 1 )
    }
  )
  
  output$map <- renderLeaflet({
    leaflet() %>%
      addTiles(urlTemplate = "//{s}.tiles.mapbox.com/v3/jcheng.map-5ebohr46/{z}/{x}/{y}.png",
               attribution = 'Maps by <a href="http://www.mapbox.com/">Mapbox</a>') %>%
      setView(lng = -96.84, lat = 32.92, zoom = 6) 
  })
}
shinyApp(ui, server)

Answer 1

Try case_when as

weight = case_when(input$map_zoom <=8 ~2, input$map_zoom >8 ~3)

This works fine for me:

observeEvent(eventExpr = input$mymap_zoom, {
      print(input$mymap_zoom)           # Display zoom level in the console
      mywt <- case_when(input$mymap_zoom <=8 ~1, input$mymap_zoom >8 ~6)
      print(mywt)
      leafletProxy(
        mapId = "mymap" , session = session
      )%>%
        clearShapes() %>% 
        addCircles(data=df,lng = ~Long, lat = ~Lat,
                   weight = mywt ,
                   opacity = 1, fill = TRUE, fillOpacity = 1 )
    }
  )

You just need clearShapes()