r - 在 Shiny 页面中使用可变数量的输入字段

Question

我的问题如下:

我有一个 Shiny 的应用程序，它根据用户输入显示可变数量的输出元素(例如，详见:dynamically add plots to web page using shiny)。

但是，我还想向每个输出元素添加一个输入元素，允许用户为输出指定一些修饰符(例如，让用户选择将每个元素视为图表还是表格，但一个可以对可变数量的输出进行任何类型的修改。

我认为最简单的方法是向每个元素添加一个 selectInput 元素，其中包含我希望用户拥有的选择。我的问题是每次呈现页面时，selectInput 元素似乎都恢复到它们的初始值，因此更改它们没有效果(实际上，它们确实有瞬间效果，但随后它们被重置并且效果是还原)。

以下代码重现了该问题(根据@skasch 对上述问题的回答进行了修改):

server.R

library(shiny)
max_plots <- 5

shinyServer(function(input, output) {

# Insert the right number of plot output objects into the web page
output$plots <- renderUI({
  plot_output_list <- lapply(1:input$n, function(i) {
     modifier <- paste("select",i,sep="")
     plotname <- paste("plot", i, sep="")
     plottitle <- paste("plottitle", i, sep="")
     tablename <- paste("tablename", i, sep="")

     # By default I display a plot
     disp <- plotOutput(plotname, height = 280, width = 250)  
     # modifier may not be in the input if this is the first time the element is displayed
     if(modifier %in% names(input) && input[[modifier]] == "table") {
       disp = tableOutput(tablename)
     }
     # Make the output element display properly:
     tagList(
       textOutput(plottitle, container = h3),
       uiOutput(modifier),
       disp)
   })    
   # Convert the list to a tagList - this is necessary for the list of items
   # to display properly.
   do.call(tagList, plot_output_list)
})

# 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
        modifier <- paste("select",i,sep="")
        plotname <- paste("plot", my_i, sep="")
        plottitle <- paste("plottitle", my_i, sep="")
        tablename <- paste("tablename", 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$n, sep = ""))
        })
        output[[plottitle]] <- renderText({paste("1:", my_i, ".  n is ", input$n, sep = "")
        })
        output[[tablename]] <- renderTable({table(x = 1:my_i, y = 1:my_i)
        })
        # I suspect the problem is the re-evaluation of this part that resets the "selected" field
        output[[modifier]] <- renderUI({selectInput(
                                          inputId = modifier,
                                          label="select how to display",
                                          choices = c("plot","table"),
                                          selected = 1)})
    })
}
})

ui.r

library(shiny)
shinyUI(pageWithSidebar(

  headerPanel("Dynamic number of plots"),

    sidebarPanel(
      sliderInput("n", "Number of plots", value=1, min=1, max=5)
    ),

    mainPanel(
      uiOutput("plots") # This is the dynamic UI for the plots
    )
))

Answer 1

虽然我认为这不是一个理想的解决方案，但分配:

output[[modifier]] <- renderUI({selectInput(
                                      inputId = modifier,
                                      label="select how to display",
                                      choices = c("plot","table"),
                                      selected = input[[modifier]])})

解决了这个问题，尽管我很乐意得到一个更好的解决方案(特别是一个避免每次都重新构建输入对象的解决方案)。