如何在閃亮的應用

Question

介紹

初始化默認值呈現項目在shinyApp，我想渲染動態輸入輸出。

我的問題是，使用shinydashboard和不同的選項卡時，*Input()的默認值僅在各個選項卡被激活（想到輸入和輸出選項卡）時纔會呈現。

當在一個簡單的例子中使用input$*值的switch語句時（除非在輸入之後，switch確實工作並且輸出出現），我得到相同的行爲。請參閱以下內容：

代碼

library(shiny) 
shinyApp(
    ui = shinyUI(fluidPage(sidebarLayout(sidebarPanel(uiOutput("select_bin")), 
             mainPanel(plotOutput("distPlot"))))), 
    server = function(input, output) { 
    output$select_bin <- renderUI({ 
     selectInput("bins", "Number of bins:", c("few", "many")) 
    }) 
    output$distPlot <- renderPlot({ 
     x <- faithful[, 2] 
     bins <- switch(input$bins, few = 10L, many = 100L) 
     bins <- seq(min(x), max(x), length.out = bins) 
     hist(x, breaks = bins, col = 'darkgray', border = 'white') 
    }) 
    }) 

上述工程的代碼，而是拋出一個

Warning: Error in switch: EXPR must be a length 1 vector。

我想input$bins不可用，直到selectInput呈現。

問題

我如何定義input$bins的默認值，所以selectInput呈現之前，在renderPlot表達不會引發報警？

第一種方法

我試圖用observe爲this post，但我不知道它的確切含義，因此很難解決的問題。

library(shiny) 
shinyApp(
    ui = shinyUI(fluidPage(sidebarLayout(sidebarPanel(uiOutput("select_bin")), 
             mainPanel(plotOutput("distPlot"))))), 
    server = function(input, output) { 
    output$select_bin <- renderUI({ 
     selectInput("bins", "Number of bins:", c("few", "many")) 
    }) 
    observe({ 
     bins <- switch(input$bins, few = 10L, many = 100L) 
     bins 
    }) 
    output$distPlot <- renderPlot({ 
     x <- faithful[, 2] 
     bins <- seq(min(x), max(x), length.out = bins) 
     hist(x, breaks = bins, col = 'darkgray', border = 'white') 
    }) 
    }) 

哪一個根本不起作用並拋出額外的Warning: Error in seq.default: object 'bins' not found。

Answer 1

使用

• reactiveValues創建缺省值的列表，並
• observeEvent爲input$bins，更新默認

似乎解決了問題：

library(shiny) 
shinyApp(
    ui = shinyUI(fluidPage(sidebarLayout(sidebarPanel(uiOutput("select_bin")), 
             mainPanel(plotOutput("distPlot"))))), 
    server = function(input, output) { 
    values <- reactiveValues(bins = 10L) 
    output$select_bin <- renderUI({ 
     selectInput("bins", "Number of bins:", c("few", "many")) 
    }) 
    observeEvent(input$bins, { 
     values$bins <- switch(input$bins, few = 10L, many = 100L) 
    }) 
    output$distPlot <- renderPlot({ 
     x <- faithful[, 2] 
     bins <- seq(min(x), max(x), length.out = values$bins) 
     hist(x, breaks = bins, col = 'darkgray', border = 'white') 
    }) 
    }) 

Answer 2

需要。只有input$bins不爲空時，req()纔會告訴閃爍以呈現該圖。

library(shiny) 
shinyApp(
    ui = 
shinyUI(fluidPage(sidebarLayout(sidebarPanel(uiOutput("select_bin")), 
            mainPanel( 
plotOutput("distPlot"))))), 
    server = function(input, output) { 
    output$select_bin <- renderUI({ 
     selectInput("bins", "Number of bins:", c("few", "many")) 
    }) 
    output$distPlot <- renderPlot({ 
     req(input$bins) 
     x <- faithful[, 2] 
     bins <- switch(input$bins, few = 10L, many = 100L) 
     bins <- seq(min(x), max(x), length.out = bins) 
     hist(x, breaks = bins, col = 'darkgray', border = 'white') 
    }) 
    })