What's wrong with this Shiny code? Ggplot does not render, dropdown menu does-CodePudding

I am learning how to use Shiny, and I tried to create a very simple barchart in ggplot2, with a dropdown menu, that allows the user to select a class from a school using the dropdown, and it is supposed to create a barchart with exam result percentages on the y-axis and names on the x-axis. The code I have is as follows:

ui = fluidPage(selectInput(inputId = "Class", label = "Pick a Class", choices = levels(fulldata$Class), plotOutput("bar"), multiple = FALSE, selectize = FALSE))

server = function(input, output){
  
  output$bar = renderPlot({
    plotdata = reactive({data %>% filter(Class == input$Class)})
    ggplot(plotdata(), aes(x = Name, y = Percent_full)   geom_bar())
    })
  }
shinyApp(ui = ui, server = server)

The end result correctly renders the dropdown menu, but it does not render the plot whatsoever. I have tried changing the ggplot call to a simple hist(rnorm(1000)) but it does not render either.

CodePudding user response：

I solved the problem: the plotOutput function in the fluidPage function was defined as an argument of the input function, not as an argument of fluidPage. It works now!

CodePudding user response：

It might be that your code needs to declare the reactive data before you create your ggplot.

Try this:

plotdata = reactive(
data %>% filter(Class == input$Class)
)

output$bar = renderPlot({
    ggplot(plotdata(), aes(x = Name, y = Percent_full)   geom_bar())
})

Here is more example code from a functioning shiny app using reactive data for ggplot:

data <- reactive(
  merged_clean_data %>% filter(between(date, as.POSIXct(input$dateRange[1]),
                   as.POSIXct(input$dateRange[2])))
)

 #Output plot for any selected variable
    output$timePlot <- renderPlot({
      ggplot(data(), aes(x = date, !!input$selection))  
        theme_classic()   geom_line()  
        coord_cartesian(xlim = as.POSIXct(ranges$x, origin = "1970-01-01"), expand = FALSE)  
        theme(text = element_text(size = 16), axis.title.x=element_blank(), axis.text.y = element_text(angle=90, vjust=1, hjust=1))   {if(input$hlineadd)geom_hline(yintercept = input$hline)}   
        {if(input$smoothingadd)geom_smooth()} 
    }, res = 80)