shiny leaflet display labels based on zoom level - r

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
)