Tabsets and changing sidebarpanel widgets

server.r

library(shiny)

shinyServer(function(input,output)({
  
  ## Get the value of the dataset that is selected by user from the list of datasets
  data <- reactive({
    get(input$dataset)
  })
  
  ## to output the dataset
  output$dat <- renderDataTable({
    data()
  })
  
  # Pulling the list of variable for choice of variable x
  output$varx <- renderUI({
    selectInput("variablex", "select the X variable", choices=names(data()))
  })
  
  # Pulling the list of variable for choice of variable y
  output$vary <- renderUI({
    selectInput("variabley", "select the Y variable", choices=names(data()))
    
  })

  ## Pulling the factor or categorical variables from the dataset  
  output$factor <- renderUI({
    t = split(names(data()),sapply(data(), function(x) paste(class(x), collapse=" ")))
    selectInput("cat", "select the categorical variable", choices=t[[1]])
    
  })
  


}))

ui.r

library(shiny)
shinyUI(pageWithSidebar(
  headerPanel("Conditional Panels"),
  sidebarPanel(
    selectInput("dataset", "select the desired dataset", choices=ls('package:datasets'), selected = "mtcars"),
    
    conditionalPanel(condition="input.tabselected==1",
uiOutput("varx"),
uiOutput("vary")
    ),
    
    conditionalPanel(condition="input.tabselected==2",
                    uiOutput("factor")
    ) 
  ),
  mainPanel(
    tabsetPanel(
      tabPanel("Data", value=0, dataTableOutput("dat")),
      tabPanel("Plot", value=1), 
      tabPanel("Subset Data", value=2)
      , id = "tabselected"
    )
  )
))