Shiny-server，openxlsx 绘图无法插入

Question

当使用 runApp() 从控制台运行以下闪亮应用程序时，它会按预期工作，显示绘图并提供下载嵌入绘图的 Excel 文件的功能。在闪亮的服务器上运行相同的应用程序会产生错误

无法打开文件“Rplots.pdf”

• 闪亮服务器 v1.4.2.786
• Node.js v0.10.40
• R 版本 3.3.1 (2016-06-21) -- “你头发里的虫子”

• Ubuntu 14.04.4 LTS

  library(shiny)
  library(openxlsx)
  library(magrittr)
  
  # Define UI for application that draws a histogram
  ui <- shinyUI(fluidPage(
  
     # Application title
     titlePanel("Old Faithful Geyser Data"),
  
     # Sidebar with a slider input for number of bins 
     sidebarLayout(
        sidebarPanel(
           sliderInput("bins",
                       "Number of bins:",
                       min = 1,
                       max = 50,
                       value = 30),
           downloadButton('specDataDownload',
                          label = "Download",
                          class = NULL)
        ),
  
        # Show a plot of the generated distribution
        mainPanel(
           plotOutput("distPlot")
        )
     )
  ))
  
  # Define server logic required to draw a histogram
  server <- shinyServer(function(input, output) {
  
     output$distPlot <- renderPlot({
        # generate bins based on input$bins from ui.R
        x    <- isolate({faithful[, 2] })
        bins <- seq(min(x), max(x), length.out = input$bins + 1)
  
        # draw the histogram with the specified number of bins
        hist(x, breaks = bins, col = 'darkgray', border = 'white')
  
     })
     output$specDataDownload <- downloadHandler(
         filename = function() {
             paste("ProcessedPlateAssay",
                   gsub("-|[[:space:]]|:",
                        "",
                        Sys.time()),
                   ".xlsx",
                   sep = "_")
         },
         content = function(con) {
             x    <- isolate({faithful[, 2] })
             bins <- seq(min(x), max(x), length.out = input$bins + 1)
             output <- createWorkbook()
             addWorksheet(
                 output,
                 "One")
             hist(
                 x,
                 breaks = bins,
                 col = 'darkgray',
                 border = 'white')
             insertPlot(
                 output,
                 sheet = 1,
                 startRow = (1),
                 startCol = 5,
                 width = 6.5,
                 height = 3,
                 fileType = "png",
                 units = "in",
                 dpi = 600)
  
         saveWorkbook(
             wb = output,
             file = con
         )
         })
  })
  
  # Run the application 
  shinyApp(ui = ui, server = server)
  

Answer 1

我想提供一个最小的例子，因为我一直在努力解决openxlsxsinsertPlot函数在闪亮服务器内无法工作的问题，可能是由于tempfile或 的权限问题dev.copy。对我来说最有效的方法是使用ggsave，因为它可以非常巧妙地处理分辨率，并且还有一个比例参数，可以调整图像元素的大小，使其更适合演示。我还提供了使用该函数的第二种方法png。

下面是一个可重现的示例，部分取自@sebkopf 在“保存在闪亮应用程序中制作的绘图”中的答案

library(shiny)
library(openxlsx)
library(ggplot2)

ui <- fluidPage(
  downloadLink("downloadExcel", "Excel Graph Download")
)

server <- function(input, output) {

  p1 <- qplot(mpg, data=mtcars, geom="density", fill=as.factor(gear), 
alpha=I(.5), main="Distribution of Gas Mileage")
  p2 <- qplot(age, circumference, data = Orange, geom = c("point", "line"), 
colour = Tree)

  output$downloadExcel <- downloadHandler(
    filename = "savePlot.xlsx",
    content = function(file){
      wb <- createWorkbook()

      addWorksheet(wb, "ggsave", gridLines = F)
      addWorksheet(wb, "png", gridLines = F)

      # Method 1: using ggsave

      ggsave("p1.png", plot = p1, scale = .6) # Scale parameter resizes the object making text more legible
      ggsave("p2.png", plot = p2, scale = .6)

      insertImage(wb, "ggsave", "p1.png", width = 5, height = 3.5)
      insertImage(wb, "ggsave", "p22.png", startCol = "J", width = 16, height = 10, units = "cm")

      # Method 2: using png function

      png("p11.png")
      print(p1)
      dev.off()

      insertImage(wb, "png", "p11.png", width = 5, height = 3.5)

      png("p22.png")
      print(p2)
      dev.off()

      insertImage(wb, "png", "p22.png", startCol = "J", width = 16, height = 10, units = "cm")

      saveWorkbook(wb, file, overwrite = T)

      unlink(c("p1", "p2", "p11", "p22")) # To remove the images from the server
    }
  )
}

shinyApp(ui, server)