R Shiny中的环境 [英] Environments in R Shiny

问题描述

在 http://shiny.rstudio.com/articles/scoping.html 解释光泽范围的规则得到了很好的解释.彼此嵌套有3个环境或级别:函数内，会话内和所有会话内可用的对象.使用<-将在您所处的环境中更改对象，而<<-将在全局(即针对所有会话)中更改对象.

At http://shiny.rstudio.com/articles/scoping.html the rules for scoping in shiny are well explained. There are 3 environments or levels nested inside each other: objects available within a function, within a session and within all sessions. Using <- will change the object within the environment you are in and <<- will change it globally i.e. for all sessions.

如果我在会话中定义变量但想从函数中更改该变量怎么办?

What if I define a variable within the session but want to change it from within a function?

<-只会在函数内对其进行更改，因此其他功能无法读取，并且<<-将在所有会话中对其进行更改.之间没有什么?像只是上一层"?

<- will just change it within the function so not readable by other functions and <<- will change it for all sessions. Is there nothing inbetween? Like "just one level up"?

推荐答案

感谢您对Stephane的引用.如果在shinyServer()之前定义了对象，则在shinyServer()内的任何地方使用<<-将会更改应用程序所有实例的值.如果对象是在ShinyServer()中定义的，则<< ;-(在函数内部或外部)只会更改该应用实例的值.

Thanks for that reference Stephane. If an object is defined before the shinyServer() then using <<- anywhere within shinyServer() will change the value for all instances of the app. If the object is defined within shinyServer() then <<- (inside or outside a function) will only change the value for that instance of the app.

我将一个带有计数器和实例ID的小应用程序组合在一起进行测试.运行该应用程序的两个实例并在它们之间进行切换以增加计数，这证明了<<-

I put together a little app with a counter and instance ids to test this. Running two instances of the app and switching between them increasing the count demonstrates the effect of <<-

ui.r

    library(shiny)

shinyUI(pageWithSidebar(

  headerPanel("Testing Environments"),

  sidebarPanel(


    actionButton("increment_counter", "Increase Count")


  ),

  mainPanel(

    tabsetPanel(
      tabPanel("Print", verbatimTextOutput("text1"))


      ))

))

server.r

instance_id<-1000

shinyServer(function(input, output, session) {

  instance_id<<-instance_id+1
  this_instance<-instance_id

  counter<-0


  edit_counter<-reactive({

    if(input$increment_counter>counter){
    counter<<-counter+1
    }

    list(counter=counter)

  })



  output$text1 <- renderPrint({ 
    cat(paste("Session ID: ",Sys.getpid()," \n"))
    cat(paste("Global Instance ID: ",instance_id," \n"))
    cat(paste("This Instance ID: ",this_instance," \n"))
    cat(paste("Button Value: ",input$increment_counter," \n"))
    cat(paste("Counter Value: ",edit_counter()$counter," \n"))


  })



}) # end server function

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