Lambo Lambo - 1 month ago 6
R Question

Change setView dynamically according to select box in R shiny app

I'm developing a leaflet map in R shiny. In this app I want the focus of the map to be changed whenever the lng and lat value in

setView()
is changed. The lng and lat values are based on what country I select from a drop down box. Previously I use static value for lng and lat in an
ifelse()
function and the app works. But now the problem is when I want to make things more generic: the lng and lat will be the mean of the longitude and latitude from a subset of the data with the chosen country, the app doesn't show map anymore (from my point of view the calculation seems right)

Below is the simplified and workable R script:

global.R:

library(devtools)
library(leaflet)
library(htmlwidgets)
library(shiny)
library(shinydashboard)
library(sp)
library(rworldmap)
library(RCurl)
library(ggmap)

df <- read.csv(url("https://docs.google.com/spreadsheets/d/1rrEJiuxr4nafTqUQBlPpUdGwvGeGtBJExlPJdday2uw/pub?output=csv"),
header = T,
stringsAsFactors = F)
df$Time <- as.Date(df$Time, "%d/%m/%Y")


ui.R

header <- dashboardHeader(
title = 'Shiny Memery'
)
body <- dashboardBody(
fluidRow(
tabBox(
tabPanel("My Map", leafletOutput("mymap",height = 550)),
width = 700
))
)
dashboardPage(
header,
dashboardSidebar(
sliderInput('Timeline Value','Time line',min = min(df$Time),
max = max(df$Time),
value = c(min(df$Time), min(df$Time)+10)),
selectInput("select_country", label = "Select Country",
choices = NULL,
selected = NULL)
),
body
)


server.R

shinyServer(function(input, output, session) {

dfs <- reactive({
tmp <- subset(df, df$Time <= input$`Timeline Value`[2] & df$Time >= input$`Timeline Value`[1])
tmp
})

part_choices <- reactive({
as.list(c("All", unique(as.character(dfs()$Country))))
})

observe({
updateSelectInput(session, "select_country", choices=part_choices())
})

output$mymap <- renderLeaflet({
lng <- ifelse(input$select_country == "All", mean(dfs()$lon),
mean(subset(dfs(), Country %in% input$select_country)$lon)
)
lat <- ifelse(input$select_country == "All", mean(dfs()$lat),
mean(subset(dfs(), Country %in% input$select_country)$lat)
)

m <- leaflet(dfs()) %>%
addTiles(
) %>%
setView(lng, lat, zoom = 5) %>%
addMarkers(~lon, ~lat,
clusterOptions = markerClusterOptions())
})
})


You will see in the server.R part I use
ifelse()
to change the lng and lat value that later can be used in
setView()
function. After I changed the else argument into a calculation the app doesn't work anymore.

Really appreciate if someone can tell me where I was wrong.

Thanks in advance.

Answer

In your ui.R, try changing your country input to

selectInput("select_country", label = "Select Country", 
            choices = "All", 
            selected = "All")

My guess is that the ifelses do not return a number, given that input$select_country is initialized at NULL, which (for reasons that are unclear to me) causes both renderLeaflet and updateSelectInput not to run, preventing the country selector from being updated.