基于 Shinydashboard 中的计时器更新传单标记

Question

我有数据框df，它有两个变量lat 和lon，现在我需要创建一个Shinydashboard，它通过在每个10 seconds 之后从数据框中获取下一行值来更新地图。

df

 df <- data.frame("Lat" = c(12.8882, 12.890, 12.891), "Lon" = c(77.58195,77.58190,77.581958))

Ui.R

library(shiny)
library(leaflet)
shinyUI( fluidPage(
                leafletOutput("map1")
                   )
        )

server.R

library(shiny)

 shinyServer(function(input, output, session) {

 output$mymap <- renderLeaflet({
                      leaflet() %>%
                        addTiles() %>%  # Add default OpenStreetMap map tiles
                        addMarkers(lng=df$lon, lat=df$lat)})
                               })

我只知道我可以使用invalidateLater() 来调用计时器，但我不知道如何实现它以增量读取数据框中的行。

Expected Result

我需要一张地图，其中marker 在每个10 Seconds 之后移动到下一个位置，移动标记的坐标通过数据框df 给出。

Answer 1

您可以使用reactiveVal() 来跟踪当前显示的标记，并将observe() 与invalidateLater() 和leafletProxy() 结合使用来删除先前的标记并添加新的标记。为此，我们可以在每次添加标记时给图层一个layerId，然后我们可以在绘制下一个标记时使用它再次删除标记。

下面给出了一个工作示例，我添加了一些 cmets 来说明正在发生的事情。希望这会有所帮助！

---

---

library(shiny)
library(leaflet)
set.seed(1)

df <- cbind(rnorm(40) * 2 + 13, rnorm(40) + 48)

ui <- fluidPage(
  leafletOutput("mymap")
)

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

  # Create the base map
  output$mymap <- renderLeaflet({
    leaflet() %>%
      addProviderTiles(providers$Stamen.TonerLite,
                       options = providerTileOptions(noWrap = TRUE)
      ) %>%
      setView(lng = mean(rnorm(1000) * 2 + 13), lat =  mean(rnorm(1000) + 48), zoom = 7)
  })

  # Initialize a reactiveVal to keep track of which point is currently selected
  point_to_plot <- reactiveVal(1)

  observe({
    # invalidate every 2 seconds
    invalidateLater(2000)
    isolate({
      # update point_to_plot() to next value. If next value is higher than the amount of rows
      # in df, set it to 1.
      point_to_plot(ifelse(point_to_plot()+1<=nrow(df),point_to_plot()+1,1))
      # Use leafletProxy to remove our previous marker, and add the new one.
      leafletProxy('mymap') %>%
        removeMarker('my_marker') %>%
        addMarkers(layerId = 'my_marker',data = df[point_to_plot(),,drop=F])
    })
  })

}

shinyApp(ui, server)

---

编辑：使用您的数据的工作示例：

library(shiny)
library(leaflet)
set.seed(1)

df <- data.frame("Lat" = c(12.8882, 12.890, 12.891), "Lon" = c(77.58195,77.58190,77.581958))

ui <- fluidPage(
  leafletOutput("mymap")
)

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

  # Create the base map
  output$mymap <- renderLeaflet({
    leaflet() %>%
      addProviderTiles(providers$Stamen.TonerLite,
                       options = providerTileOptions(noWrap = TRUE)
      ) %>%
      setView(lat = 12.89, lng = 77.58195, zoom = 14)
  })

  # Initialize a reactieVal to keep trakc of which point is currently selected
  point_to_plot <- reactiveVal(1)

  observe({
    # invalidate every 2 seconds
    invalidateLater(2000)
    isolate({
      # update point_to_plot() to next value. If next value is higher than the amount of rows
      # in df, set it to 1.
      point_to_plot(ifelse(point_to_plot()+1<=nrow(df),point_to_plot()+1,1))
      # Use leafletProxy to remove our previous marker, and add the new one.
      leafletProxy('mymap') %>%
        removeMarker('my_marker') %>%
        addMarkers(layerId = 'my_marker',data = df[point_to_plot(),,drop=F])
    })
  })

}

shinyApp(ui, server)