如何避免在用if else子句呈现表的第一行时出现闪亮的R错误“argument is of length zero”

我写了一个闪亮的申请表。我想展示桌子的第一行。当我上传一个Excel文件或CSV时,这是有效的,但是当我上传一个SAS7BDAT或XPT文件时,我得到错误: argument is of length zero . 这个堆栈交换 Answer 建议我需要测试零和NA。我也试过,测试 qctable 但我还是收到了错误。有趣的是,如果我上传一个CSV或Excel文件,然后再上传一个s a s文件(任何一个),它都能正常工作。

相关代码:

#outputs the first row of the input file.
  output$firstrow <- renderText({
    req(qctable())
    if (filext() %in% c('.csv', '.txt')) {
      return(head(read_lines(input$qcfile$datapath), 1))
    } else if (
      (filext() %in% c('.xpt', '.sas7bdat')) | # This line and the next seem to be the issue
      (filext() %in% c('.xls', '.xlsx') & input$headers == TRUE)
    ) {
      return(paste0(names(qctable())))
    } else if ((filext() %in% c('.xls', '.xlsx') & input$headers == FALSE)) {
      return(paste0(qctable()[1,]))
    } else {
      return('Invalid file type!')
    }
  })

我可以通过将SAS文件条件和Excel文件条件作为不同的测试包含在 if 但这看起来很笨拙。

就像这样:

  #outputs the first row of the input file.
  output$firstrow <- renderText({
    req(qctable())
    if (filext() %in% c('.csv', '.txt')) {
      return(head(read_lines(input$qcfile$datapath), 1))
    } else if (filext() %in% c('.xpt', '.sas7bdat')) {
      return(paste0(names(qctable()), collapse=('  ')))
    } else if (filext() %in% c('.xls', '.xlsx') & input$headers == TRUE) {
      return(paste0(names(qctable()), collapse=('  ')))
    } else if ((filext() %in% c('.xls', '.xlsx') & input$headers == FALSE)) {
      return(paste0(qctable()[1,], collapse=('  ')))
    } else {
      return('Invalid file type!')
    }
    })

也许还需要注意的是,如果上载的文件类型无效,则会发生相同的错误,但如果先上载CSV/Excel,则会正常工作。

完整代码:

#### Libraries ####
library(shiny)
library(tidyverse)
library(readxl)
library(haven)

#### UI ####
ui <- fluidPage(
  # Sidebar with a slider input for number of bins 
  sidebarLayout(
    sidebarPanel(
      width = 3,
      # Input: Select a file 
      fileInput("qcfile", "Choose a File to QC",
                multiple = FALSE,
                accept = c("text/csv",
                           "text/comma-separated-values,text/plain",
                           ".csv",
                           '.txt',
                           '.xlsx',
                           '.xls',
                           '.xpt',
                           '.sas7bdat')),
      # Choose Separator
      htmlOutput('delimrb'),
      # Choose header values
      htmlOutput('header'),
      # Choose column TDxs are stored
      tags$strong('File Extension:'),
      verbatimTextOutput('file_ext')
    ),
    # Creates Main Panel with relevant tabs 
    mainPanel(width = 9,
      tabsetPanel(
        type = 'tabs',
        tabPanel('1st Row', verbatimTextOutput('firstrow'))
      ))
  )
)

#### Server #### 
server <- function(input, output) {
  #determines input file extention
  filext <- reactive({
    req(input$qcfile)
    fext <- tolower(str_extract(as.vector(input$qcfile$datapath), '\\.[^.]+$'))
    return(fext)
  })

  output$file_ext <- renderText(filext())

  # Sets UI for delimiter if input file is .csv or .txt
  output$delimrb <- renderUI({
    req(input$qcfile)
    if (filext() %in% c('.csv', '.txt')) {
      radioButtons("delimiter", "Delimiter for CSV/TXT",
                   choices = c(comma = ',',
                               pipe = '|',
                               tab = '\t')
      )
    }
  })

  # Sets UI for header if input file is not sas/xpt
  output$header <- renderUI({
    req(input$qcfile)
    if (filext() %in% c('.csv', '.txt', '.xlsx', '.xls')) {
      radioButtons('headers', 'Header row present?',
                   choices = c('Yes' = TRUE,
                               'No' = FALSE))
    }
  })

  #outputs the first row of the input file.
  output$firstrow <- renderText({
    req(qctable())
    if (filext() %in% c('.csv', '.txt')) {
      return(head(read_lines(input$qcfile$datapath), 1))
    } else if (
      (filext() %in% c('.xpt', '.sas7bdat')) | # This line and the next seem to be the issue
      (filext() %in% c('.xls', '.xlsx') & input$headers == TRUE)
    ) {
      return(paste0(names(qctable())))
    } else if ((filext() %in% c('.xls', '.xlsx') & input$headers == FALSE)) {
      return(paste0(qctable()[1,]))
    } else {
      return('Invalid file type!')
    }
  })

  # Creates Table from input file
  qctable <- reactive({
    req(input$qcfile)
    if (filext() %in% c('.csv', '.txt')){
      return(read_delim(file = input$qcfile$datapath,
                        delim = input$delimiter,
                        col_names = as.logical(input$headers),
                        col_types = cols(.default = 'c'))
      )
    } else if (filext() %in% c('.xls', '.xlsx')) {
      return(read_excel(path = input$qcfile$datapath,
                        col_names = as.logical(input$headers),
                        col_types = 'text'))
    } else if (filext() %in% c('.xpt')) {
      return(read_xpt(file = input$qcfile$datapath))
    } else if (filext() %in% c('.sas7bdat')){
      return(read_sas(data_file = input$qcfile$datapath))
    }
  })

}

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