Use reactive expressions in renderPlot and download handler

问题

I have had an issue by using the same reactive expression in renderPlot() and in downloadHandler(). I want to use the same reactive expression to minimize maintenance later. I have created two examples which create very simple figures (mwe1 creates a jpeg which you can download, mwe2 does not). I prefer a solution which uses a creative expression which can be both used by renderPlot() and downloadHander() as in mwe2. Is anybody able to help me with this?

Thanks in advance!

mwe1 <- function() {


app = list(
    ui = bootstrapPage(
        fluidPage(
            sidebarPanel(
                sliderInput("mean", "choose mean", -10, 10, 1),
                sliderInput("sd", "choose sd", 0, 5, 1)),
            mainPanel(
                plotOutput("hist"),
                downloadButton("histDownload")

                )
        )
    ),
    server = function(input, output) {

        output$hist <- renderPlot(hist(rnorm(1000, input$mean, input$sd)))

        .hist <- reactive(hist(rnorm(1000, input$mean, input$sd)))

        output$histDownload <- downloadHandler(
            filename = function() {
                paste("hist.jpg")
            }, 
            content = function(file) {
                jpeg(file, quality = 100, width = 800, height = 800)
                .hist()
                dev.off()
            }
        )

    }

)
runApp(app)
}


mwe2 <- function() {


app = list(
    ui = bootstrapPage(
        fluidPage(
            sidebarPanel(
                sliderInput("mean", "choose mean", -10, 10, 1),
                sliderInput("sd", "choose sd", 0, 5, 1)),
            mainPanel(
                plotOutput("hist"),
                downloadButton("histDownload")

            )
        )
    ),
    server = function(input, output) {

        output$hist <- renderPlot(.hist())

        .hist <- reactive(hist(rnorm(1000, input$mean, input$sd)))

        output$histDownload <- downloadHandler(
            filename = function() {
                paste("hist.jpg")
            }, 
            content = function(file) {
                jpeg(file, quality = 100, width = 800, height = 800)
                .hist()
                dev.off()
            }
        )

    }

)
runApp(app)
}

回答1:

Change mwel2 to:

mwe2 <- function() {


  app = list(
    ui = bootstrapPage(
      fluidPage(
        sidebarPanel(
          sliderInput("mean", "choose mean", -10, 10, 1),
          sliderInput("sd", "choose sd", 0, 5, 1)),
        mainPanel(
          plotOutput("hist"),
          downloadButton("histDownload")

        )
      )
    ),
    server = function(input, output) {


      output$hist <- renderPlot(.hist())

      .hist <- reactive(hist(rnorm(1000, input$mean, input$sd)))

      output$histDownload <- downloadHandler(
        filename = function() {
          paste("hist.jpg")
        }, 
        content = function(file) {
          jpeg(file, quality = 100, width = 800, height = 800)
          plot(.hist())
          dev.off()
        }
      )

    }

  )
  runApp(app)
}

So call plot again on the .hist object.

来源：https://stackoverflow.com/questions/24157990/use-reactive-expressions-in-renderplot-and-download-handler

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