將selectInput存儲在字符串/字符對象中

Question

我想將輸入$ var中的變量存儲到一個對象，該對象可以與后者的字符串進行比較。 現在，我只是試圖通過將其存儲到對象value_stored中在屏幕上打印。 但是它不打印任何內容*（錯誤：無法將類型'closure'強制轉換為類型'character'*的向量）。 這意味着它沒有存儲值。

library(shiny)
ui <- fluidPage(
  titlePanel("censusVis"),

  sidebarLayout(
    sidebarPanel(
      helpText("Create demographic maps with 
               information from the 2010 US Census."),

      selectInput("var", 
                  label = "Choose a variable to display",
                  choices = c("Percent White", 
                              "Percent Black",
                              "Percent Hispanic", 
                              "Percent Asian"),
                  selected = "Percent White")
      ),

    mainPanel(
      textOutput("selected_var")
      textOutput("test")
    )
  )
  )

server <- function(input, output) {

  output$selected_var <- renderText({ 
    paste(input$var)
  })

  value_store <- reactive(input$var)

  output$test <- renderText({
   paste(value_store) 
  })

  # I want to use the value in input$var for some comparision. 
  # but value_store unable to store. Help.

}


shinyApp(ui = ui, server = server)

Answer 1

我強烈建議使用reactiveValues （對象來存儲你的反應值）和observeEvent 。

使用服務器代碼：

server <- function(input, output) {
    # Create object for reactive values 
    rv <- reactiveValues(
        value_store = character()
    )
    # When input changes -> update
    observeEvent(input$var, {
        output$selected_var <- renderText({ 
            paste(input$var)
        })
        rv$value_store <- input$var
        output$test <- renderText({
            paste(rv$value_store) 
        })
    })
}

PS：您可以刪除paste因為它在那里沒有任何作用。

Answer 2

差不多了，您只需要先定義反應性元素，然后在watchEvent（）函數中監視輸入即可。 然后，在觀察值內部，使用isolate（）更新值。

ui <- fluidPage(
  titlePanel("censusVis"),

  sidebarLayout(
    sidebarPanel(
      helpText("Create demographic maps with 
           information from the 2010 US Census."),

  selectInput("var", 
              label = "Choose a variable to display",
              choices = c("Percent White", 
                          "Percent Black",
                          "Percent Hispanic", 
                          "Percent Asian"),
              selected = "Percent White")
  ),

 mainPanel(
   textOutput("selected_var")
   textOutput("test")
 )
 )
)

server <- function(input, output) {

  value_store <- reactive(val = '')

  observeEvent(input$var, {

    # add to reactive
    isolate(value_store$val = input$var)

    # or render update
    output$selected_var <- renderText({ 
       paste(value_store$val)
     })

  })




 output$test <- renderText({
   paste(value_store$val) 
 })

  # I want to use the value in input$var for some comparision. 
  # but value_store unable to store. Help.

}


shinyApp(ui = ui, server = server)