title: shiny app "expr_sub" is missing error
body: <p>Here is the code for my shiny app:</p>
  
  <h1>ui.r</h1>
  
  <pre><code>shinyUI(navbarPage("My Application",id="main",
  tabPanel
  (
      "Select Data range",
      sidebarLayout
      (
          sidebarPanel
          (
              selectInput("select_sector", label = h3("Select Sector"),choices = list("Sector 1" = 1, "Sector 2" = 2,"Sector 3" = 3), selected = 1),br(),
              dateRangeInput("dates_range_input", label = h3("Select Date range")),br(),
              actionButton("action_proceed1", label = "Proceed to select resolution")
          ),
          mainPanel(tableOutput("first"))
      )
  ),
  tabPanel
  (
      "Select Resolution",
      sidebarLayout
      (
          sidebarPanel
          (
              numericInput("XGRID", label = h3("Select X-Grid Size"), value = 2),br(),
              numericInput("YGRID", label = h3("Select Y-Grid Size"), value = 2),br(),
              numericInput("outlier_removal", label = h3("Outlier Removal"), value = 2),br(),
              numericInput("frequency", label = h3("Frequency"), value = 2),br(),
              actionButton("action_proceed2", label = "Proceed to Service Parameters")
          ),
          mainPanel("Here will be the image for marketing purpose")
      )
  )
  ))
  </code></pre>
  
  <h1>server.r</h1>
  
  <pre><code>shinyServer(function(input, output,session) {
      output$first &lt;- renderTable
      ({
          data.frame(x=1:100,y=1:100)
  
      })
  
     observe({
     if (input$action_proceed1&gt;0) {
     updateTabsetPanel(session, "main", selected = "Select Resolution")
     } 
     })
     })
  </code></pre>
  
  <p>I was expecting the output as the data frame defined but receiving an unexpected error:</p>
  
  <pre><code> argument "expr_sub" is missing, with no default
  </code></pre>
  
  <p>Please suggest what I am doing wrong here. I was going to put there a data set using input variables but receiving teh same error that's why for the sake of simplicity I replaced the data frame.</p>