R Shiny：按计划更新 .csv 输入

Question

我有一个每分钟自动更新新数据的 .csv。我想让 R Shiny 每小时用这个新数据集重新更新一次。

根据我所见，这将涉及 invalidateLater 或 autoInvalidate；但是，我不确定如何让这些工作（或者更重要的是，将它们放在哪里）。

ui.R 非常简单，所以我不会包含它。 server.R 如下：

library(ggplot2)
library(reshape2)
library(scales)

# data <- reactive({ # data refresh once a day # 86400000ms is 1 day  
#   invalidateLater(10000, session) # 10s to test
# })

shinyServer(function(input, output, session) {

  autoInvalidate <- reactiveTimer(10000, session)

  observe({
    x <- read.csv("wait_times.csv", header=T, stringsAsFactors=FALSE)
    x <- rename(x, c("Fall.River" = "Fall River", "Martha.s.Vineyard" = "Martha's Vineyard", "New.Bedford" = "New Bedford", "North.Adams" = "North Adams", "South.Yarmouth" = "South Yarmouth"))
    cities <- colnames(x)[-1]

    x[x == 999] <- NA

    x_long <- melt(x, id.var="timestamp") ### does not work after Attleboro ###
    x_long <- rename(x_long, c("variable" = "city", "value" = "wait_time"))
    x_long$timestamp <- strptime(x_long$timestamp, "%d/%m/%Y %H:%M %p")

    weeks <- as.double(difftime(x_long$timestamp[1], x_long$timestamp[length(x_long$timestamp)], units = "weeks")) + 1

    print("REFRESHING CSV!")
    autoInvalidate()
  })

  # pass server-side code into initial UI page
  output$cities <- renderUI({
    checkboxGroupInput("cities", 
                       label = h3("Which cities to view?"),
                       as.list(cities),
                       selected = "Boston")
  })

  output$weeks <- renderUI({
    sliderInput("weeks", 
                label = h3("How many prior weeks to average?"),
                min = 1,
                max = weeks,
                step = 1,
                value = 1)
  })

  output$main <- renderPlot({

    x_output <- x_long[x_long$city == input$cities, ]
    p <- ggplot(x_output, aes(x=timestamp, y=wait_time, group=city)) + geom_line(aes(color=city), size=1.5) + scale_x_datetime(breaks = date_breaks("10 min")) + theme(axis.text.x = element_text(angle = 90, hjust=1), legend.position = "bottom") + labs(x=NULL, y="Waiting time (minutes)")
    print(p)

  })

})

当我从 .csv 中提取某些值时（如 "weeks" 和 "cities"），R Shiny 说它们不存在：

Error in as.list(cities) : object 'cities' not found
Error in sliderInput("weeks", label = h3("How many prior weeks to average?"),  : 
  object 'weeks' not found
Error in func() : object 'x_long' not found

我认为正在发生的事情是，由于这些是在 observe 函数中声明的，因此它们被它封装了。或许我应该早点invalidating/declaring这些？我试过在声明 shinyServer() 之前放置它们，但这似乎也没有用。

我研究了这些来源，但无法复制：

https://github.com/Btibert3/nhl-shiny/blob/master/server.R
Update graph/plot with fixed interval of time
http://shiny.rstudio.com/reference/shiny/latest/reactiveTimer.html

Answer 1

observe 不是 return 值（它 return 是观察者参考 class）。您想改用 reactive。

例如，如果您只想要变量 cities，您可以这样做：

refrehed_cities <- reactive({
    autoInvalidate()

    x <- read.csv("wait_times.csv", header=T, stringsAsFactors=FALSE)
    x <- rename(x, c("Fall.River" = "Fall River", "Martha.s.Vineyard" = "Martha's Vineyard", "New.Bedford" = "New Bedford", "North.Adams" = "North Adams", "South.Yarmouth" = "South Yarmouth"))
    cities <- colnames(x)[-1]
    return cities
)}

然后在checkboxGroupInput中使用它：

output$cities <- renderUI({
     checkboxGroupInput("cities", 
                       label = h3("Which cities to view?"),
                       as.list(refreshed_cities()),
                       selected = "Boston")
    })
})

另一种方法是使用函数 reactiveValues，它使您能够存储反应值。

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