R 中的 react 性与玩具示例 Shiny

Question

我正在修改这个例子(https://gist.github.com/wch/5436415/)。下面是一个玩具模型。基本上，我需要 selectInput 是响应式的，每次更改 selectInput 时，选择的值都会传递给 global.r 中的函数。然后我需要能够使用结果。

基本上:
(1) 当应用程序首次出现时，应该有 1 个情节

(2) 当用户更改 slider 输入时，server.r 中的 max_plots 函数中有一个响应式“input$n”。这个 input$n 被传递给 global.r 中的“NumberOfPlots”函数

(3) "numberOfPlots"将返回一个数字。前任。如果用户将选择输入更改为 5。5 被传递给“NumberOfPlots”，而 5 从“NumberOfPlots”返回

(4) 既然用户做出了选择，我在 Shiny 的服务器函数中使用“maxplots()”来访问绘图的数量

我收到错误消息:

Error in .getReactiveEnvironment()$currentContext() : 
  Operation not allowed without an active reactive context. (You tried to do something that can only be done from inside a reactive expression or observer.)

下面是我的代码，如果你创建一个“runshiny.r”文件并调用下面的 4 行，你可以运行它:

install.packages("shiny")
library(rJava)
library(shiny)
runApp("C://Users/me/multi")#change this to the path of your correct folder

这是我的 server.r

shinyServer(function(input, output,session) {

#get the number of plots from reactive input and pass to global function
max_plots<- reactive({
  print("IN reactive function")
  NumberOfPlots(input$n)
})


  # Insert the right number of plot output objects into the web page
  output$plots <- renderUI({
    #plot_output_list <- lapply(1:input$n, function(i) {
    plot_output_list <- lapply(1:max_plots(), function(i) {
      plotname <- paste("plot", i, sep="")
      plotOutput(plotname, height = 280, width = 700)
    })
    # Convert the list to a tagList - this is necessary for the list of items
    # to display properly.
    do.call(tagList, plot_output_list)
  }) #end of output$plots

  # Call renderPlot for each one. Plots are only actually generated when they
  # are visible on the web page.
  for (i in 1:max_plots()) {
    # Need local so that each item gets its own number. Without it, the value
    # of i in the renderPlot() will be the same across all instances, because
    # of when the expression is evaluated.
    local({
      my_i <- i
      plotname <- paste("plot", my_i, sep="")

      output[[plotname]] <- renderPlot({

        plot(1:my_i, 1:my_i,
             xlim = c(1, max_plots()),
             ylim = c(1, max_plots()),
             main = paste("1:", my_i, ".  n is ", input$n, sep = "")
        )
      })#end of renderPlot
    })#end of local
  }#end of loop over max_plots

  })#end of server

这是我的 global.r

NumberOfPlots<-function(n)
{
  print("in global") 
  print(n)
  length(seq(from=1 , to=n, by = 1))
}

这是我的 ui.r

shinyUI(pageWithSidebar(
  headerPanel("Dynamic number of plots"),
  sidebarPanel(
    sliderInput("n", "Number of plots", value=1, min=1, max=7)
  ),
  mainPanel(
    # This is the dynamic UI for the plots
    uiOutput("plots")
  )
))

Answer 1

你需要结束你的for循环到 observe() .