R Shiny：eventReactive和renderUI交互

Question

I'm trying to do a similar app to this one Shiny: dynamic dataframe construction; renderUI, observe, reactiveValues. I would like to create an option to select, for example, the number of cylinders in the list. So that the table is automatically updated after selecting the number. Could someone explain to me what I'm doing wrong? As you can see on the graphics program does not work well.

My code:

ui:

library(shiny)

hw <- mtcars

shinyUI(fluidPage(
  title = 'Examples of DataTables',
  sidebarLayout(
    sidebarPanel(

      radioButtons(
        inputId="radio",
        label="Variable Selection Type:",
        choices=list(
          "All",
          "Manual Select"
        ),
        selected="All"),

      conditionalPanel(
        condition = "input.radio != 'All'",
        selectizeInput(
          'show_vars', 
          'Columns in cars to show:',
          choices=names(hw), 
          selected = names(hw),
          multiple =TRUE),

        uiOutput("category1")
      )

    ),
    mainPanel(
      verbatimTextOutput("summary"), 
      tabsetPanel(
        id = 'dataset',
        tabPanel('hw', dataTableOutput('mytable1'))
      )
    )
  )
))

server:

library(shiny)
library(ggplot2)

shinyServer(function(input, output) {


  Data <- reactive({

    if(input$radio == "All"){
      hw
    } else {
      hw[,input$show_vars,drop=FALSE]
    }

  })

  output$category1 <- renderUI({
    selectizeInput('cat1', 'Select cyl:', choices = c("All",sort(as.character(unique(hw$cyl)))),selected = "All")

  })

  df_subset <- eventReactive(input$cat1,{
    if(input$cat1=="All") {df_subset <- hw}
    else{df_subset <- hw[hw$Position == input$cat1,]}
  })


  output$mytable1 <- renderDataTable({
     df_subset()
      hw[, input$show_vars, drop = FALSE]
  })
})

Answer 1

Here is the dashboard for your example:

# Packages
library(shiny)
library(DT)
library(dplyr)

# UI
ui <- fluidPage(   
  # Application title
  titlePanel("Example"),

  # Sidebar
  sidebarLayout(
     sidebarPanel(selectInput("si_cylinders", "Cylinders", 
                 choices = sort(unique(mtcars$cyl)), selected = "4")),
     mainPanel(dataTableOutput("dt_mtcars"))))

  # Server
  server <- function(input, output) {

  # Data set for output
  df_mtcars <- reactive({
    # 1. Read UI element
    cylinder_selected <- as.numeric(input$si_cylinders[1])

    # 2. Filter data set
    df <- mtcars %>% filter(cyl == cylinder_selected)

   # 3. Return result
   return(df)
  })

  # 2. Data table for output
  output$dt_mtcars <- renderDataTable({
    datatable(df_mtcars())
  })

 }

# Run the application 
shinyApp(ui = ui, server = server)