Shiny：SelectizeInput 选项的条件更新问题

Question

我想选择一个对输出有影响的选项。这里有两个选项：汽车，气缸可供选择。根据选择的选项，他们有不同的选择。

library(shiny)

mtcars$cars <- rownames(mtcars)

ui <- fluidPage(
  title = 'Select experiment',
  sidebarLayout(
    sidebarPanel(
      radioButtons("selectOpt", "Want to select:",
                   list("Car"='car', "Cylinders"='cyl'),
                   selected = 'car'),

      conditionalPanel(
        condition = "input.selectOpt=='car'",
        selectizeInput(
          inputId = "sel_car", 
          label = "Select a Car",
          choices = mtcars$cars
        )),
      conditionalPanel(
        condition = "input.selectOpt=='cyl'",
        selectizeInput(
          inputId = "sel_cyl", 
          label = "Select Cylinders",
          choices = unique(mtcars$cyl)
        )
        )
    ),
    mainPanel(
      helpText('Output of the examples in the left:'),
      verbatimTextOutput('ex_out')
    )
  )
)

server <- function(input, output) {

    output$ex_out <- renderPrint({
      if(!is.null(input$sel_car)){
        cat(input$sel_car,input$sel_cyl,'\n')
        mtcars[mtcars$cars == input$sel_car,]
      }else if(!is.null(input$sel_cyl)){
        mtcars[mtcars$cyl == input$sel_cyl,]
      }
    })
}

shinyApp(ui, server)

但是，我观察到这两个选项总是选择一个选项。这可以在输出的第一行中观察到（来源cat(input$sel_car,input$sel_cyl,'\n')）。

当Car被选中时，Cylinders option中的第一个选项6也被选中。

选择缸选项，汽车选项 MAZDA RX4 EM>的首选也被选中。

如何避免第一个选项的默认选择，以便我能够同时评估 if 和 else if 部分？

Answer 1

单选select(ize)Input() 总是有一个选定的选项。 来自?selectInput：

已选择
最初选择的值（或多个值，如果 multiple = TRUE）。如果未指定，则默认为单选列表的第一个值，多选列表没有值。

要获得您需要的功能，我们可以插入一种“无效”选择：

selectizeInput(
  inputId = "sel_car", 
  label = "Select a Car",
  choices = c('No car' = 0, mtcars$cars)
)

并在if.. else 中检查：

if(input$sel_car != 0){
  cat(input$sel_car,input$sel_cyl,'\n')
  mtcars[mtcars$cars == input$sel_car,]
}

完整代码：

library(shiny)

mtcars$cars <- rownames(mtcars)

ui <- fluidPage(
  title = 'Select experiment',
  sidebarLayout(
    sidebarPanel(
      radioButtons("selectOpt", "Want to select:",
                   list("Car"='car', "Cylinders"='cyl'),
                   selected = 'car'),

      conditionalPanel(
        condition = "input.selectOpt=='car'",
        selectizeInput(
          inputId = "sel_car", 
          label = "Select a Car",
          choices = c('No car' = 0, mtcars$cars)
        )),
      conditionalPanel(
        condition = "input.selectOpt=='cyl'",
        selectizeInput(
          inputId = "sel_cyl", 
          label = "Select Cylinders",
          choices = c('No cylinder selected' = 0, unique(mtcars$cyl)),
          selected = NA
        )
      )
    ),
    mainPanel(
      helpText('Output of the examples in the left:'),
      verbatimTextOutput('ex_out')
    )
  )
)

server <- function(input, output) {

  output$ex_out <- renderPrint({
    cat(input$sel_car)
    if(input$sel_car != 0){
      cat(input$sel_car,input$sel_cyl,'\n')
      mtcars[mtcars$cars == input$sel_car,]
    }else if(input$sel_cyl != 0){
      mtcars[mtcars$cyl == input$sel_cyl,]
    }
  })
}

shinyApp(ui, server)