How do I create a reactive plot using ggplot in Shiny application

Question

I have spent several hours trying to figure out how to generate a bar plot using ggplot2 for a shiny app I want to create. The ui works fine, however; the server function generates an empty plot.

The issue is with renderPlot function. I believe I must not be passing the reactive values properly to the aes_string arguments in ggplot. C2 is a filtered dataset. The goal is to build a simple app in which the user selects a two variables, a dataset is filtered based upon those variables. The subsetted dataset is passed to ggplot data argument.

       library(shiny)
library(dplyr)


ui <- fluidPage(
  sidebarLayout(
    sidebarPanel(
      selectInput(inputId = "Demog",label = "Factor:",choices = c("HH Income" = "Income",
                                                                  "Age Group" = "Age",
                                                                  "US Region" = "Region") , selected = "Age"),
      selectInput(inputId = "Car",label = "VW Model:",choices = c("BEETLE" = "BEETLE",
                                                                  "CC" = "CC",
                                                                  "EOS" = "EOS",
                                                                  "GOLF" = "GOLF",
                                                                  "GTI" ="GOLF SPORTSWAGEN GTI",
                                                                  "JETTA" = "JETTA",
                                                                  "PASSAT" = "PASSAT",
                                                                  "TIGUAN" = "TIGUAN",
                                                                  "TOUAREG" = "TOUAREG") , selected = "BEETLE"),
      radioButtons(inputId = "Metric",label ="Measurement Type",choices = 
                     c("Conquest Volume Index" = "TotCmpConqVol_IDX","C/D Ratio" = "TotCmpCDRatio_IDX"), selected = "TotCmpConqVol_IDX" )                

    )
  ),
  mainPanel(
    tags$h1("The Bar Charts"),
    tags$h2("The metrics"),


    plotOutput("P1")

  )

)
server <- function(input, output){
  library(ggplot2)
  CONQDF <- read.csv("C:/Users/Reginald/Desktop/CONQ_VW/CONQUEST2.csv")

  C2 <- reactive(subset(CONQDF,input$Demog %in% levels(input$Demog)[1] & CONQDF$VW_Model == input$Car))

  output$P1 <- renderPlot({
    ggplot(C2(),aes_string(x="CompMake", y=input$Metric))+ geom_bar(stat = "identity")
                          })
}






shinyApp(ui,server)

Welcome to stackoverflow! You could use as example dataset for example car dataset and change choices accordingly, then code would be reproducible and you would get faster answer. — Mikael Jumppanen
if I recall correctly you should use print() when using ggplot2. So... print(ggplot(C2()...) or p1 <- ggplot(C2()...) print(p1) — Mikael Jumppanen
@Mikael Jumppanen Thank you Mikael. I tried those options and still no luck. I thank you for the fast response and I will use one of the example datasets to see if I can get the code to run. If not, I will repost my response with the example dataset. I really appreciate it. — RareAir

Michal Majka Michal Majka · Accepted Answer · 2016-07-10T09:24:53

The ui works fine, however; the server function generates an empty plot.

This is most likely due to the fact that the function subset returns an empty dataset. In order to debug the code, first, I would print out in the console this part:

C2 <- reactive(subset(CONQDF,input$Demog %in% levels(input$Demog)[1] & CONQDF$VW_Model == input$Car))

I believe that this part is wrong because input$Demog is just a character string and not a factor. That's why levels(input$Demog) = NULL and input$Demog %in% levels(input$Demog) = FALSE. Hence, as a result, you get an empty dataset.

To check this:

output$P1 <- renderPlot({
    print(C2()) # print it out to the console.
    ggplot(C2(),aes_string(x="CompMake", y=input$Metric))+ geom_bar(stat = "identity")
})

If this is the case, you only need to re-think subsetting part.

How do I create a reactive plot using ggplot in Shiny application

2 Answers