How to correctly clearShapes in Leaflet in a Shiny app

Question

Note that this question has been posted at the R Shiny Google Group :

Following the Leaflet for R/ Shiny Integration documentation , I'm getting unwanted/ unexpected behavior with the leafletProxy function.

In the app below, I'd expect the circle markers to appear/ disappear as the input$choices changes.

The reactive df 'filteredData' seems to be working correctly.

Am I incorrectly using leafletProxy() or clearShapes()?

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


my_df <- data.frame(lat = 34.72 + rnorm(1000, sd = .18), 
                    lng = -92.5 + rnorm(1000, sd = .33), 
                    category = c(rep("A", 300), rep("B", 300), rep("C", 400)))

ui <- bootstrapPage(
  tags$style(type = "text/css", "html, body {width:100%;height:100%}"),
  leafletOutput("map", height = '100%', width = '100%'),
  absolutePanel(top = 10, right = 10, 
                checkboxGroupInput("choices", "Choices", choices =     list("A","B","C"), selected = c("A","B","C")),
                verbatimTextOutput("my_rows")


  )
)


server <- function(input, output) {

  filteredData <- reactive( my_df %>% filter(category %in% input$choices) )

    output$map <- renderLeaflet({ leaflet() %>% addTiles() %>% setView(lat =     34.72, lng = -92.5, zoom = 9) })

    observe({

      leafletProxy("map", data = filteredData()) %>% clearShapes() %>% addCircleMarkers(radius = 6, weight = 1, fillColor = "red", fillOpacity = 0.3)

    })

    output$my_rows <- renderPrint({ filteredData() %>% nrow() })
}

shinyApp(ui = ui, server = server)

Answer 1

Your first issue is solved by using clearMarkers() rather than clearShapes() .

As to the other issue you pointed out, leaflet struggles with empty (and NA) data. When you deselect all the values, your data.frame obviously becomes empty. A simple check for this to stop leaflet trying to plot it will solve this issue.

Here I'm using an if - else do do the check.

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

my_df <- data.frame(lat = 34.72 + rnorm(1000, sd = .18), 
                    lng = -92.5 + rnorm(1000, sd = .33), 
                    category = c(rep("A", 300), rep("B", 300), rep("C", 400)))

ui <- bootstrapPage(
    tags$style(type = "text/css", "html, body {width:100%;height:100%}"),
    leafletOutput("map", height = '100%', width = '100%'),
    absolutePanel(top = 10, right = 10, 
                 checkboxGroupInput("choices", "Choices"
                                     , choices = list("A","B","C")
                                     , selected = c("A","B","C")),
                 verbatimTextOutput("my_rows")
    )
)

server <- function(input, output) {

    filteredData <- reactive({ 
        my_df %>% filter(category %in% input$choices) 
        })

    output$map <- renderLeaflet({ 
        leaflet() %>% 
            addTiles() %>% 
            setView(lat = 34.72, lng = -92.5, zoom = 9) 
        })

    observe({

        df <- filteredData()

        ## check for empty dataframe
        if(nrow(df) == 0){
            leafletProxy("map", data = df) %>% 
            clearMarkers()
        }else{
            leafletProxy("map", data = df) %>% 
                clearMarkers() %>% 
                addCircleMarkers(radius = 6, weight = 1
                                 , fillColor = "red", fillOpacity = 0.3)
        }

    })

    output$my_rows <- renderPrint({ 
        filteredData() %>% 
            nrow() 
        })
}

shinyApp(ui = ui, server = server)