如果对象不存在，R Shiny 忽略下载

Question

我有一个闪亮的应用程序，用户上传 5 个数据源，生成一些汇总表，然后将这些表下载到 ppt。目前，此下载仅在将所有 5 个源都加载到应用程序中时才有效。我正在尝试通过 "exists" 函数找到解决方法。

下面是只有一个文件的示例代码，演示应该适用于任何 csv 文件。

在下载处理程序部分，代码通过if (exists("file1.df"))检查数据帧是否存在，然后生成flextable。生成幻灯片的代码块也使用 if (exists("flextable_file1"))

但是，ppt 仅在上传文件时才会生成。如果 "exists" 对象不存在，为什么不忽略代码部分？

library(shiny)
library(tidyverse)
library(flextable)
library(officer)

ui <- fluidPage(

  # Side bar layout and inputs ----
  sidebarLayout(
    sidebarPanel(

      h4("Attach file"),
      fileInput("file1", "File location", accept = c(".csv")),

      downloadButton("download_powerpoint", "Download Tables to Powerpoint")
    ),

    mainPanel(tableOutput("file1.df"))
  )
)

server <- function(input, output, session) {

  # LMS Pivot ----
  file1.df <- reactive({

    req(input$file1)

    read.csv(input$file1$datapath)
  })

  output$file1.df <- renderTable({
    file1.df()
  })   

  # PPT ----

  output$download_powerpoint <- downloadHandler(
    filename = function() {  
      "test.pptx"
    },
    content = function(file) {

      if (exists("file1.df")) { 

        flextable_file1 <- flextable(file1.df()) %>% 
          border_remove() %>% 
          border(border.top = fp_border(color = "black"),
                 border.bottom = fp_border(color = "black"),
                 border.left = fp_border(color = "black"),
                 border.right = fp_border(color = "black"), part = "all") %>% 
          align(align = "center", part = "all")
      }

      example_pp <- read_pptx() %>% 
        add_slide(layout = "Title Slide", master = "Office Theme") %>% 
        ph_with_text(
          type = "ctrTitle",
          str = "Weekly P3 Deck"
        ) %>% 
        ph_with(
          location = ph_location_type(type = "subTitle"),
          value = "Copy and paste the generated tables into your report"
        ) 

      # LMS slide ----
      if (exists("flextable_file1")) { 

        example_pp <- example_pp %>% add_slide(layout = "Title and Content", master = "Office Theme") %>% 
          ph_with_text(
            type = "title",
            str = "words"
          ) %>% 
          ph_with_flextable(
            value = flextable_file1,
            type = "body"
          ) 
      }

      print(example_pp, target = file)
    }
  )

}

shinyApp(ui, server)

Answer 1

我找到了解决办法。而不是使用 if exists 使用 if else 到 return null 如果它没有上传 else return df.

if (is.null(input$file1)) {

        NULL

      } else {

flextable_file1 <- flextableformatting

如果对象不存在，R Shiny 忽略下载

Rshiny Ignore download if object not present

r

shiny

officer