title: R shiny app is not reactive
body: <p>I have been working with the Shiny package, there is one function, which the user is able to select from a list of choices, based on the choice, the plot will update. however, right now the app does not update when the selection changes. </p>
  
  <pre><code>server.R
  ----------
  library(shiny)
  library(quantmod)
  library(TTR)
  
  shinyServer(function(input, output, session) {
  
    selectedsymbol &lt;- reactive({
      symbol &lt;- input$selectstock
    })
  
    output$stockplotoverview &lt;- renderPlot({
      symbolinput &lt;- selectedsymbol()
      getSymbols(symbolinput)
      chartSeries(get(symbolinput))
      addMACD()
      addBBands()
    })
  
    output$candlechart &lt;- renderPlot({
      symbolinput &lt;- input$selectstock
      getSymbols(symbolinput)
      candleChart(get(symbolinput),multi.col=TRUE,theme="white")
    })
  
    output$barchart &lt;- renderPlot({
      symbolinput &lt;- input$selectstock
      getSymbols(symbolinput)
      barChart(get(symbolinput)) 
    })
  
  })
  
  ui.R
  library(shiny)
  
  shinyUI(fluidPage(
  
    # Application title
    titlePanel("Hello Shiny!"),
  
    # Sidebar component
    sidebarLayout(
      sidebarPanel(
        selectInput("selectstockset", label = h3("Select the stock set"), choices = list("My Stock set" = 1, 
                                                                                          "Good Stock Set" = 2,
                                                                                          "Customize" = 3), selected = 1),
        selectInput("selectalgo", label = h3("Select the algorithm"), choices = list("Worst Increment" = 1, 
                                                                                          "PAMR" = 2,
                                                                                          "SMA" = 3), selected = 1),
        dateRangeInput("daterange", label = h3("Date Range")),
        submitButton("Simulate")
  
      ),
  
      # Show a plot of the generated distribution
      mainPanel(
        tabsetPanel(
          tabPanel("Stock Set",
                     helpText("Select a stock to examine. 
                              Information will be collected from yahoo finance."),
  
                   textInput("stocksetname", label = h4("Stock Set Name"), 
                             value = "Enter text...") ,
  #                  uiOutput("selectstock"),
                   selectInput("selectstock", label = h4("Select the stock"), choices = list("AAPL" = "AAPL",
                                                                                              "SBUX" = "SBUX",
                                                                                              "GS" = "GS")),
                   tabsetPanel(
                     tabPanel("Overview",
                              plotOutput("stockplotoverview")
                              ),
                     tabPanel("Candle Chart",
                              plotOutput("candlechart")
                              ),
                     tabPanel("Bar Chart",
                              plotOutput("barchart"))
                   ),
  
                  hr(),
                  fluidRow(
                    column(3,
                           actionButton("addtostockset","Add to stock set"),
                           tags$style(type='text/css', "#addtostockset { align: right;}")
                    ),
                    column(3,
                           actionButton("confirm","Confirm stock set"),
                           tags$style(type='text/css', "#confirm { align: right; }")
                    )
                  )),
          tabPanel("Simulation Window"),
          tabPanel("Statistical Result")
      )
    )
  )))
  </code></pre>