闪亮，R - 错误：无法从非数字矩阵推导坐标

Question

我正在尝试使用 R 的 Shiny 包在地图上绘制点，因为它们全天出现在不同的点。

当 Shiny 服务器被告知获取子集数据帧的坐标（经纬度）时，会出现意外问题：

coordinates(selected.tweet.points.spdf) <- ~ lon + lat

有趣的是，这在 Shiny 之外有效，但在 Shiny 中不适合我。

Shiny 窗口中显示的错误信息是：

Error: cannot derive coordinates from non-numeric matrix

如果您要在非空间对象上调用 coordinates() 而不告诉它要考虑什么坐标，这与 会出现相同的错误消息，如下所示：

coordinates(selected.tweet.points.spdf)

这是一个可重现性极低的示例（没有实际绘图）：

library(shiny)
library(tigris)
library(dplyr)
library(leaflet)
library(sp)
library(ggmap)
library(maptools)
library(broom)
library(httr)
library(rgdal)
library(tidyr)

nyc.neighborhoods.url <- GET('http://data.beta.nyc//dataset/0ff93d2d-90ba-457c-9f7e-39e47bf2ac5f/resource/35dd04fb-81b3-479b-a074-a27a37888ce7/download/d085e2f8d0b54d4590b1e7d1f35594c1pediacitiesnycneighborhoods.geojson')
nyc.neighborhoods.spdf <- readOGR(content(nyc.neighborhoods.url, 'text'), 'OGRGeoJSON', verbose = F)
nyc.neighborhoods.df <- tidy(nyc.neighborhoods.spdf)

tweet.points.df <- data.frame(class = c("Not Private", "Not Private", "Private", "Private", "Private", "Private"),
                        lat = c(40.65514, 40.65514, 42.74662, 42.74662, 40.65514, 40.57238),
                        lon = c(-73.94878, -73.94878, -75.77004, -75.77004, -73.94878, -74.15395),
                        time = c("14:00", "14:00", "14:30", "14:30", "14:30", "14:30"))

shinyApp(
  # User interface
  ui = fluidPage(
    titlePanel("Social Media Post Privacy Classifier"),
    sidebarLayout(
      sidebarPanel(
        sliderInput("time", "Time of day (by half hour)",   
                    min = as.POSIXlt("2017-01-01 00:00:00", tz = "GMT"),   
                    max = as.POSIXlt("2017-01-01 23:30:00", tz = "GMT"),   
                    value = as.POSIXct("2017-01-01 00:00:00", tz = "GMT"),   
                    timeFormat="%H:%M", timezone = "+0000", step = 60 * 30, animate = T)
      ),
      mainPanel(
        textOutput("out")
      )
    )
  ),
  # Server
  server = function(input, output) {
    choropleth.selection <- reactive({
      selected.time <- format(input$time, '%H:%M')
      selected.tweet.points.df <- tweet.points.df[tweet.points.df$time == selected.time, ]
      selected.tweet.points.spdf <- selected.tweet.points.df
      coordinates(selected.tweet.points.spdf) <- ~ lon + lat
      proj4string(selected.tweet.points.spdf) <- proj4string(nyc.neighborhoods.spdf)
      selected.tweet.points.df.matches <- over(selected.tweet.points.spdf, nyc.neighborhoods.spdf)
      selected.tweet.points.df <- cbind(selected.tweet.points.df, selected.tweet.points.df.matches)
      selected.tweet.points.df <- selected.tweet.points.df %>% drop_na()
      print(selected.tweet.points.df$class)
    })
    output$out <- renderPrint({ choropleth.selection() })
  }
)

这是一个例子，证明了同样的技术在 Shiny 之外也有效：

selected.time <- "14:30"
points.df <- data.frame(class = c("Not Private", "Not Private", "Private", "Private", "Private", "Private"),
                        lat = c(40.65514, 40.65514, 42.74662, 42.74662, 40.65514, 40.57238),
                        lon = c(-73.94878, -73.94878, -75.77004, -75.77004, -73.94878, -74.15395),
                        time = c("14:00", "14:00", "14:30", "14:30", "14:30", "14:30"))
points.df <- data.frame(points.df[points.df$time == selected.time, ])
coordinates(points.df) <- ~ lon + lat

Answer 1

当selected.tweet.points.spdf 为空时，即没有匹配时间时会出现错误。在初始运行中就是这种情况，当selected.time 是00:00 - 没有匹配的tweet.points.df$time。

一种可能的解决方案是像这样更改您的服务器功能：

server = function(input, output) {
    choropleth.selection <- reactive({
      selected.time <- format(input$time, '%H:%M')
      selected.tweet.points.df <- tweet.points.df[tweet.points.df$time == selected.time, ]
      selected.tweet.points.spdf <- selected.tweet.points.df
      validate(need(nrow(selected.tweet.points.df)>0, "No match")) # <=======
      coordinates(selected.tweet.points.spdf) <- ~ lon + lat
      proj4string(selected.tweet.points.spdf) <- proj4string(nyc.neighborhoods.spdf)
      selected.tweet.points.df.matches <- over(selected.tweet.points.spdf, nyc.neighborhoods.spdf)
      selected.tweet.points.df <- cbind(selected.tweet.points.df, selected.tweet.points.df.matches)
      selected.tweet.points.df <- selected.tweet.points.df %>% drop_na()
      print(selected.tweet.points.df$class)
    })
    output$out <- renderPrint({ choropleth.selection() })
  }