Shiny Leaflet map with reactive slider input

Question

I have a dataset looking something like this:

Dataset <- data.frame(
  "Type" = c("A", "B", "A", "B"),
  "Value" = c(1000000, 200, 4000000, 150),
  "Lat" = c(40.7, 41.8, 42.4, 43.1), 
  "Long" = c(-3.2, -2.1, -1.6, -3.1)
)

Type    Value   Lat   Long
 A     1000000  40.7  -3.2
 B       200    41.8  -2.1
 A     4000000  42.4  -1.6
 B       150    43.1  -3.1

I'm displaying each point as a marker in a leaflet map using Lat and Long as coordinates, but as you can see the Value range varies a lot depending on Type. To make my map more user-friendly I enabled a pickerInput() to let me choose the Type to be displayed on the map and then a sliderInput() to choose the Value. Using reactive() I filter the points for the map.

My problem is that I'm unable to make a reactive sliderInput() range depending on the Type selected in pickerInput. I only managed to get a slider covering the whole range, which in the example data above would be from 150 to 4000000.

I would need to get a slider from 150 to 200 and from 1000000 to 4000000 depending on the pickerInput. My code so far:

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

ui <- bootstrapPage(
  absolutePanel(top = 10, right = 10,
   sliderInput("range", "Value", min(Dataset$Value, na.rm = TRUE), max(Dataset$Value, na.rm = TRUE),
      value = range(Dataset$Value, na.rm = FALSE), step = 1000),
    pickerInput("Type", "Type", choices = c("A", "B"),      selected = c("A", "B"), multiple = T, options = list(`actions-box` = TRUE)),
  ),
  leafletOutput("map", width = "50%")
)

server <- function(input, output) {
  
  filteredData <- reactive({
    Dataset %>% 
    filter(Type %in% input$Type) %>%
    filter(Value >= input$range[1]) %>% 
    filter(Value <= input$range[2])
 })

  output$map <- renderLeaflet({
    leaflet(Dataset) %>% addTiles() %>% addMarkers(data = filteredData(), lng = ~Long, lat = ~Lat)
  })
}

shinyApp(ui, server)

Answer 1

You can use updateSliderInput() (and more generally update*() functions when you want to update the choices). Don't forget to add session in function(input, output). Here, we can filter the data in two steps:

• first, we choose the type. This will determine the range of the slider.

• second, after the slider is updated, we choose the range.

Here's the full example:

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

Dataset <- data.frame(
  "Type" = c("A", "B", "A", "B"),
  "Value" = c(1000000, 200, 4000000, 150),
  "Lat" = c(40.7, 41.8, 42.4, 43.1), 
  "Long" = c(-3.2, -2.1, -1.6, -3.1)
)
ui <- bootstrapPage(
  absolutePanel(
    top = 10,
    right = 10,
    sliderInput(
      "range",
      "Value",
      min(Dataset$Value, na.rm = TRUE),
      max(Dataset$Value, na.rm = TRUE),
      value = range(Dataset$Value, na.rm = FALSE),
      step = 1000
    ),
    pickerInput(
      "Type",
      "Type",
      choices = c("A", "B"),
      selected = c("A", "B"),
      multiple = T,
      options = list(`actions-box` = TRUE)
    ),
  ),
  leafletOutput("map", width = "50%")
)

server <- function(input, output, session) {
  
  filter_type <- reactive({
    Dataset %>%
      filter(Type %in% input$Type)
  })
  
  observeEvent(input$Type, {
    updateSliderInput(
      session = session,
      inputId = "range",
      min = min(filter_type()$Value),
      max = max(filter_type()$Value),
      value = range(filter_type()$Value, na.rm = FALSE)
    )
  })
  
  filter_range <- reactive({
    filter_type() %>% 
      filter(Value >= input$range[1]) %>% 
      filter(Value <= input$range[2])
  })
  
  output$map <- renderLeaflet({
    leaflet(Dataset) %>% 
      addTiles() %>% 
      addMarkers(data = filter_range(), lng = ~Long, lat = ~Lat)
  })
}

shinyApp(ui, server)