r - 根据 Shinydashboard 中的计时器更新传单标记

Question

我有数据框 df其中有两个变量 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 map 。 .
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)})
                               })

我唯一知道的是我可以使用 invalidateLater()调用计时器，但我不知道如何为数据帧中的行的增量读取实现它。
Expected Result
我需要一张 map 在哪里 marker每隔 10 Seconds 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()跟踪当前显示的标记，并使用 observe()结合 invalidateLater()和 leafletProxy()删除前一个标记并添加新标记。为此，我们可以给图层一个 layerId每次我们添加标记时，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，我添加了一些注释来说明正在发生的事情。希望这可以帮助!

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)

EDIT: Working example with your data:

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)