shiny leaflet display labels based on zoom level

Question

I want to display my marker labels based on zoom level. Based on (https://rstudio.github.io/leaflet/shiny.html) I tried to use "input$MAPID_zoom". In my example, labels stored in location_name should be displayed when zoom level (mapscale) is lower to 6.

What I tried :

library(shiny)
library(leaflet)

 # my data
df <- data.frame(
  location_name = c('S1', 'S2'),
  lng = c(-1.554136,  -2.10401),
  lat = c(47.218637, 47.218637), 
  stringsAsFactors = FALSE)


# UI
 ui <- shinyUI(fluidPage(
  leafletOutput('map')

  ))

# server 

server <- shinyServer(function(input, output, session) {

  mapscale <-  observe({
    input$map_zoom   # get zoom level
  })


  output$map <- renderLeaflet({
    leaflet() %>%
    addTiles() %>% 
    addMarkers(data=df, lng = ~lng, lat = ~lat,
               label =~if(mapscale<6, location_name))
})

})

shinyApp(ui = ui, server = server)

Answer 1

A few remarks on your code if you like. If you wrap the zoom in a reactive function, reference it like mapscale(). Use the normal if statement in R and the ~ in front of the variable. Then you should be fine.

Reproducible example:

library(shiny)
library(leaflet)

df <- data.frame(
  location_name = c('S1', 'S2'),
  lng = c(-1.554136,  -2.10401),
  lat = c(47.218637, 47.218637), 
  stringsAsFactors = FALSE
)


ui <- shinyUI(
  fluidPage(
    leafletOutput(outputId = 'map')
  )
)

server <- shinyServer(function(input, output, session) {

  output$map <- renderLeaflet({
    leaflet() %>%
      addTiles()
  })

  observeEvent(
    eventExpr = input$map_zoom, {
      print(input$map_zoom)           # Display zoom level in the console
      leafletProxy(
        mapId = "map", 
        session = session
      ) %>% 
        clearMarkers() %>%
        addMarkers(
          data = df, 
          lng = ~lng,
          lat = ~lat,
          label = if(input$map_zoom < 6) ~location_name
      )
    }
  )


})

shinyApp(
  ui = ui, 
  server = server
)