r - 响应式(Reactive)过滤数据以生成 map

Question

在使用 mapview 处理 Shiny 的 map 时，我对 react 感到困惑，并试图让我的 map 动态更新。这是一个可重现的示例，尽管是使用其他 SO 答案的原则设计的，但无法正常工作:

#
# This is a Shiny web application. You can run the application by clicking
# the 'Run App' button above.
#
# Find out more about building applications with Shiny here:
#
#    http://shiny.rstudio.com/
#

library(shiny)
library(sf)
library(mapview)

# Define UI for application that draws a histogram
ui <- fluidPage(

    # Application title
    titlePanel("Test of Mapview Selective Viewing"),

    # Sidebar with a slider input for number of bins 
    sidebarLayout(
        sidebarPanel(
         selectInput("county", "County Name",
                    choices = c("All", levels(franconia$NAME_ASCI)),
                    selected = "All"
         )

        ),

        # Show a plot of the generated distribution
        mainPanel(
           mapviewOutput("mapPlot")
        )
    )
)

# Define server logic required to draw a histogram
server <- function(input, output) {

    fran <- reactive({
        f <- franconia
        if(input$county != "All") f <- franconia %>% filter(NAME_ASCI == input$county)

        f
    })

    output$mapPlot <- renderMapview({

        #get the data
        f <- isolate(fran())

        #generate a map
        mapview(f, zcol = "NAME_ASCI")
    })
}

# Run the application 
shinyApp(ui = ui, server = server)

这可行，但 map 不会更新。我尝试放入一个操作按钮 - 并将 input$button 放在isolate语句之前，但是，这会导致整个事情抛出错误。

我要么想看所有的东西，要么想看一个县。

对于这里缺少/错误的内容有什么想法吗？我对 Shiny 和处理 react 有点陌生!

Answer 1

使用 renderMapview 似乎在某种程度上“不鼓励”(参见 https://github.com/r-spatial/mapview/issues/160#issuecomment-398130788; https://github.com/r-spatial/mapview/issues/58 )。您应该在 mapview 对象的 @map 属性上使用 renderLeaflet。这应该有效:

library(shiny)
library(sf)
library(mapview)
library(leaflet)

# Define UI for application that draws a histogram
ui <- fluidPage(
  
  # Application title
  titlePanel("Test of Mapview Selective Viewing"),
  
  # Sidebar with a slider input for number of bins 
  sidebarLayout(
    sidebarPanel(
      selectInput("county", "County Name",
                  choices = c("All", levels(franconia$NAME_ASCI)),
                  selected = "All"
      )
      
    ),
    
    # Show a plot of the generated distribution
    mainPanel(
      mapviewOutput("mapPlot")
    )
  )
)

# Define server logic required to draw a histogram
server <- function(input, output) {
  
  fran <- reactive({
    f <- franconia
    if(input$county != "All") f <-  f <- franconia[franconia$NAME_ASCI == input$county, ] 
    
    f
  })
  
  output$mapPlot <- renderLeaflet({
    
    #get the data
    f <- fran()
    
    #generate a map
    mapview(f, zcol = "NAME_ASCI")@map
  })
}

# Run the application 
shinyApp(ui = ui, server = server)

(请注意，我还必须按照 @Kent Johnson 的建议删除 isolate 调用)

呵呵!