如何在Shiny应用的mapview/leaflet中实现单个点位的可视化

我有一个大型数据集，这里用3条记录构建了最小化可复现示例。目前我的Leaflet地图能同时显示全部3个站点，但需求是点击下拉选择框时，每次仅展示单个站点（比如只显示site2）。我知道switch函数，但不清楚怎么在这个场景里实现。附上可复现代码和数据如下：

数据预览 #

Location            geometry
* <chr>            <POINT [°]>
1 site1    (-115.1682 44.3943)
2 site2    (-114.0403 44.6845)
3 site3    (-114.8841 44.1533)

原可复现代码 #

library(shiny)
library(mapview)
library(writexl)
library(tidyverse)
library(leaflet)

locations <- c("site1", "site2", "site3") 
ui <- fluidPage(

#titlePanel("Screwtraps and temp logger in Idaho"),
sidebarLayout(
sidebarPanel(
selectInput(inputId = "site",
           label = "Select Site",
                   choices = locations)),
    mainPanel(leafletOutput("map",width = "100%", height="87vh") 
    )
   )
 )
 
server <- function(input, output, session) {
  session$onSessionEnded(function() {
    stopApp()
  })
  
  output$map<-renderLeaflet({
 #Select all sites
    final <- mapview(site, col.regions='red', alpha=1) 
   final@map 
   #How can I render my map with only the selected site from the userInput dropdown?

    })
}

shinyApp(ui, server)

数据集结构 #

site <- structure(list(Location = c("site1", "site2", "site3"), geometry = structure(list(
    structure(c(-115.1682, 44.3943), class = c("XY", "POINT", 
    "sfg")), structure(c(-114.0403, 44.6845), class = c("XY", 
    "POINT", "sfg")), structure(c(-114.8841, 44.1533), class = c("XY", 
    "POINT", "sfg"))), n_empty = 0L, precision = 0, crs = structure(list(
    input = "EPSG:4326", wkt = "GEOGCRS[\"WGS 84\",\n    DATUM[\"World Geodetic System 1984\",\n        ELLIPSOID[\"WGS 84\",6378137,298.257223563,\n            LENGTHUNIT[\"metre\",1]]],\n    PRIMEM[\"Greenwich\",0,\n        ANGLEUNIT[\"degree\",0.0174532925199433]],\n    CS[ellipsoidal,2],\n        AXIS[\"geodetic latitude (Lat)\",north,\n            ORDER[1],\n            ANGLEUNIT[\"degree\",0.0174532925199433]],\n        AXIS[\"geodetic longitude (Lon)\",east,\n            ORDER[2],\n            ANGLEUNIT[\"degree\",0.0174532925199433]],\n    USAGE[\n        SCOPE[\"Horizontal component of 3D system.\"],\n        AREA[\"World.\"],\n        BBOX[-90,-180,90,180]],\n    ID[\"EPSG\",4326]]"), class = "crs"), bbox = structure(c(xmin = -115.1682, 
ymin = 44.1533, xmax = -114.0403, ymax = 44.6845), class = "bbox"), class = c("sfc_POINT", 
"sfc"))), row.names = c(NA, 3L), sf_column = "geometry", agr = structure(c(Location = NA_integer_), class = "factor", .Label = c("constant", 
"aggregate", "identity")), class = c("sf", "tbl_df", "tbl", "data.frame"
))

site

示意图 #

不需要用switch函数，直接根据下拉框输入筛选sf数据集即可。核心是在renderLeaflet中，根据input$site过滤site数据，只保留选中的站点，再用mapview渲染。

修改后的server部分代码如下：

server <- function(input, output, session) {
  session$onSessionEnded(function() {
    stopApp()
  })
  
  output$map<-renderLeaflet({
    # 筛选选中的站点
    selected_site <- site %>% filter(Location == input$site)
    # 仅渲染选中的站点
    final <- mapview(selected_site, col.regions='red', alpha=1) 
    final@map 
  })
}

补充说明 #

• 你的数据是sf格式，用dplyr::filter可轻松根据Location列匹配下拉框输入值input$site
• 每次下拉框选择变化时，renderLeaflet会自动重新执行，渲染对应的单个站点
• 如果非要用switch函数，也可以这么写（但筛选方式更简洁）：

output$map<-renderLeaflet({
    selected_site <- switch(input$site,
                           "site1" = site %>% filter(Location == "site1"),
                           "site2" = site %>% filter(Location == "site2"),
                           "site3" = site %>% filter(Location == "site3"))
    final <- mapview(selected_site, col.regions='red', alpha=1) 
    final@map 
  })

内容的提问来源于stack exchange，提问作者Salvador