title: R shiny, cannot set column names with Shiny reactive variable for ggplot
body: <p>I recently start building shiny app but I got stuck. Please help me.Thank you in advance</p>
  
  <p>I am trying to create a bar chart to show the count for different type of cash and different term. This part, the code went well. </p>
  
  <p>And I also want to create the box plot to show the numeric summary for different variables selected by the user. I created a selectInput called "metric" and then create a reactive  called "metric1" in server.R. and then use "metric1" as the variables I selected to create box plot in server.R. </p>
  
  <p>But it keep saying "cannot find the function "metric1". I don't know why it regards "metric1" as a function? it should be a vector-name of the variable selected by the user. 
  And if I use input$metric in ggplot to create box plot directly, it still say Error: " object 'input' not found". Why cannot find input? I have paste the code below. It is not a long code. And please help me!</p>
  
  <pre><code>library(shiny)
  library(ggplot2)
  
  cash &lt;- read.csv("cash 042014-032015.csv")
  cash$TERM &lt;- as.numeric(cash$TERM)
  
  shinyServer(function(input, output) {
  
    dataset &lt;- reactive({cash[cash$mapped_name %in% (input$model),]})
    metric1 &lt;- reactive({input$metric})
  
    output$caption &lt;- renderText({
      input$model
    })
  
    output$countPlot &lt;- renderPlot({    
      p &lt;- ggplot(dataset(), aes(Incentive.Type, fill=factor(Incentive.Type))) + geom_bar()+ facet_grid(~TERM, margins=TRUE)+theme(axis.text.x =     element_blank(),axis.ticks=element_blank(),legend.text =     element_text(size=20))+guides(fill=guide_legend(title="Incentive     Type"),title.theme=element_text(size=30))+scale_x_discrete(limits=c("Standard","Standard+Captive","Standard+Customer","Standard+Captive+Customer","Special","Special+Captive","Special+Customer","Special+Captive+Customer"))
      print(p)    
    })
  
    output$summaryPlot &lt;- renderPlot({
      p &lt;- ggplot(dataset(),aes(factor(Incentive.Type), metric1()))+geom_boxplot()
      print(p)
    })
  })
  </code></pre>
  
  <p>Here is the ui.R</p>
  
  <pre><code>library(shiny)
  library(ggplot2)
  
  dataset &lt;- cash
  
  shinyUI(
  
    fluidPage(    
  
  # Give the page a title
  titlePanel("Incentives by Model"),
  
  # Generate a row with a sidebar
    sidebarPanel(
      checkboxGroupInput("model", "Select Models:", 
                  choices=c("370Z","Altima","Armada","Crew","Cube","Frontier","GTR","Juke","Leaf",
                            "Maxima","Murano","NV","Other","Pathfinder","Quest","Rogue","Sentra","Titan","Versa","Xterra"),selected="Altima"),
      selectInput("metric","Please select an option below:", choices=c("Dealer Commission Amount"="DLR_COMM_AMT", "Total Monthly Payment"="TOT_MO_PMT","Original Loan Amount"="ORIG_LN_AMT", "Rate"="RATE"), 
                  selected="DLR_COMM_AMT"),
      width=2  
    ),
  
  
  mainPanel(
    h3(textOutput("caption", container=span)),
    plotOutput("countPlot"),  
    plotOutput("summaryPlot")
  </code></pre>
  
  <p>)
  ))</p>