Leaflet/shiny: cannot draw reactive polygons

Question

Having looked through the Shiny integration example on the Leaflet for R page, I am having trouble subsetting and displaying some polygons for display in my shiny app.

At the moment, i'm getting a app, with sidebar, but the main display is simply "Error:Don't know how to get path data from object of class reactive"

The idea is to pick a country polygon from GB (3 countries) and display it alone, depending on the drop down choice;

require(shiny)
require(rgdal)
require(rgeos)
require(leaflet)

cont <- readOGR(".\\mypath\\mypolygons.shp", "mypolygons", stringsAsFactors=FALSE)

ui <- fluidPage(

  titlePanel("My page"),

  sidebarLayout(
    sidebarPanel(
      selectInput("countryInput", "Country:", choices = c('England','Scotland','Wales'))
    ),
    mainPanel(
      leafletOutput("mymap")
    )
  )
)

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

pols <- eventReactive(input$countryInput,{cont[substr(cont@data$code,1,1)==substr(input$countryInput,1,1),]})

  output$mymap <- renderLeaflet({
    leaflet() %>%
      addProviderTiles("CartoDB.Positron") %>%
      addPolygons(data = pols)
  })
}


shinyApp(ui, server)

error:

Warning: Error in polygonData.default: Don't know how to get path data from object of class reactive
Stack trace (innermost first):
    83: polygonData.default
    82: polygonData
    81: derivePolygons
    80: addPolygons
    79: function_list[[k]]
    78: withVisible
    77: freduce
    76: _fseq
    75: eval
    74: eval
    73: withVisible
    72: %>%
    71: func [#6]
    70: output$mymap
     4: <Anonymous>
     3: do.call
     2: print.shiny.appobj
     1: <Promise>

Answer 1

fix:

firstly i changed;

pols <- eventReactive(input$countryInput,{cont[substr(cont@data$code,1,1)==substr(input$countryInput,1,1),]})

to;

pols <- reactive({cont.sim[substr(cont.sim@data$gssCode,1,1)==substr(input$countryInput,1,1),]

and the 'addPolygons line was missing the open/close brackets after the variable name 'pols'

addPolygons(data = pols)

becomes

addPolygons(data = pols())