Get info from leaflet map widget object

[ArjunaCap]

How can I obtain the map bounds from an application map currently in view?

Below is my (failing) MRE; it is supposed to display a table (at right) of cities currently in the map view (at left).

Incidentally, I attempted to use the code from Mr Cheng's very fine Superzip example, but I think this leaflet is the later htmlwidget version:

Thank you

library(shiny)
 library(shinydashboard)
 library(dplyr)
 library(leaflet)
 
 ui <- dashboardPage(
   dashboardHeader(),
   dashboardSidebar(),
   dashboardBody(fluidRow(
                   box(width = 6, status = "info",
                     title = "Property Map",
                     leafletOutput("myMap")),
                   
                   box(width = 6, status = "info",
                       title = "Properties",
                       tableOutput("propsInView"))
                     
   )
  ))
 
   
  my_data <- data.frame(city = c("LA", "Chi", "Dallas", "NYC"), lat = c(34.1, 41.79, 32.82, 40.7), lng = c(-118,-87, -96.7, -74))
   
   server <- function(input, output) {
     
     ## A reactive function to update as the user adjusts the map
     # It was copied from the Superzip example
     # It doesn't work
     propsInBounds <- reactive({
       if (is.null(input$map_bounds))
         return(my_data[FALSE,])
       bounds <- input$map_bounds
       latRng <- range(bounds$north, bounds$south)
       lngRng <- range(bounds$east, bounds$west)
       subset(my_data,
              lat >= latRng[1] & lat <= latRng[2] &
                lng >= lngRng[1] & lng <= lngRng[2])
     })
       
     ## The map ##
     output$myMap <- renderLeaflet({
       leaflet(my_data) %>% addTiles() %>% addCircleMarkers()
     })
     
     ##The cities in view ##
     output$propsInView <- renderTable({
       propsInBounds() %>% select(city)
     })
     }
   
 shinyApp(ui, server)

[Joe Cheng]

Instead of input$map_bounds, try input$myMap_bounds.

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[Michael Cawthon]

That almost worked, and your timing was excellent as I was scouring the old shiny-leaflet package in github.

So I additionally needed to add id = 'myMap' when calling leaflet, as in:

 output$myMap <- renderLeaflet({
       leaflet(my_data, id = 'myMap') %>% addTiles() %>% addCircleMarkers()
     })

Thank you, Joe Cheng.

-- 

Michael Cawthon
Chief Investment Officer
Green Street Energy LLC
mcaw...@greenstenergy.com
p: 479-442-1407

[Yihui Xie]

I think we have removed the "id" argument from the leaflet() function
in the new leaflet package. If you render a map in shiny, the id
prefix will be the output id, e.g. leafletOutput(outputId), then
input$outputId_bounds, input$outputId_something, ...

Regards,
Yihui

[Joe Cheng]

That shouldn't be needed, if it doesn't work without it it's a bug. The id on leafletOutput should be enough.

[Carlos Sánchez]

Hi,

I don't think the new version of Leaflet is catching the events correctly. I have simplified Michael's code to just the Leaflet map:

library(shiny)
library(shinydashboard)
library(dplyr)
library(leaflet)

ui <- dashboardPage(
  dashboardHeader(),
  dashboardSidebar(),
  dashboardBody(fluidRow(
    box(width = 6, status = "info",
        title = "Property Map",
        leafletOutput("myMap"))

  )

  ))

server <- function(input, output) {

 
  ## The map ##

  output$myMap <- renderLeaflet({
    leaflet(my_data) %>% addTiles() %>% addCircleMarkers()
   
  })

 
  observe({
    print(input$myMap_bounds)
    print(input$myMap_shape_click)
    })
}

shinyApp(ui, server)

input$myMap_bounds works and prints out the limits of the map.

However, if I click on any of the circles nothing happens. I have also tried adding a marker but I could not get the event information for that either.

Carlos