当 fread 键参数没有特定的列名称时，R Shiny 应用程序崩溃

Question

如何从 data.table::fread 函数传递 "key" 参数而不会在上传的数据集没有该特定列名时闪亮崩溃？换句话说，如果我上传的数据集没有 "key" 列，它不会崩溃，而且它应该没有输出或只有一条警告消息。

这里我有两个数据集。第一个，test1.csv, has the key column and the second one, test2.csv，没有。

我的代码如下所示：

library(shiny)

ui <- fluidPage(
  titlePanel("Uploading Files"),
  sidebarLayout(
    sidebarPanel(
      fileInput('file1', 'Choose file to upload',
                accept = c(
                  'text/csv',
                  'text/comma-separated-values',
                  'text/tab-separated-values',
                  'text/plain',
                  '.csv',
                  '.tsv'
                )
      ),
      tags$hr(),
      checkboxInput('header', 'Header', TRUE),
      radioButtons('sep', 'Separator',
                   c(Comma=',',
                     Semicolon=';',
                     Tab='\t'),
                   ';'),
      radioButtons('quote', 'Quote',
                   c(None='',
                     'Double Quote'='"',
                     'Single Quote'="'"),
                   ''),
      tags$hr(),
      p('If you want a sample .csv or .tsv file to upload,',
        'you can first download the sample',
        a(href = 'mtcars.csv', 'mtcars.csv'), 'or',
        a(href = 'pressure.tsv', 'pressure.tsv'),
        'files, and then try uploading them.'
      )
    ),
    mainPanel(
      DT::dataTableOutput('contents')
    )
  )
)

server <- function(input, output) {

  arq <- reactiveValues(data = NULL)
  observeEvent(input$file1,{
    req(input$file1)
    arq$data <- data.table::fread(input$file1$datapath,
                                         header = input$header,
                                         sep = input$sep,
                                         quote = input$quote,
                                         key="SPECIAL")
  })

  observeEvent(input$file1,{
    output$contents = DT::renderDataTable(arq$data)
  })

}

# Run the application 
shinyApp(ui = ui, server = server)

Answer 1

你可以在读取数据时跳过key参数，然后用data.table::setkey设置密钥。

observeEvent(input$file1,{
  req(input$file1)
  dat <- data.table::fread(input$file1$datapath, header = input$header,
                           sep = input$sep, quote = input$quote)
  if ("SPECIAL" %in% names(data)){
    data.table::setkey(dat, "SPECIAL")
    arq$data <- dat
  } else {
    showModal(modalDialog("Column 'SPEACIAL' is missing"))
    arq$data <- NULL
  }
})

当 fread 键参数没有特定的列名称时，R Shiny 应用程序崩溃

R Shiny app crashes when fread key parameter doesn't have that specific column name

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