Interactive file input and reactive reading in shinyapp

Question

I would like to make a shinyapp that integrates the functionality of choosing a file (in a selected folder), (like in Interactive directory input in Shiny app (R)), and then reading it reactively by detecting changes in it, as in https://gist.github.com/wch/9652222.

However, I could not make the reactiveFileReader function work with a reactive filename (folder). It seems to work only with one pre-determined filename.

In this app, the file is expected to be chosen automatically after chosing any folder (button), provided that it is inside and has the same name of the subfolder and the extension .csv
For example, if you choose /home/name/folder, the selected file should be /home/name/folder/folder.csv
Below is a code without the expected functionality. It is showing an example file.

server<- function(input, output, session) { 
  shinyDirChoose(input, 'dir', roots = c(home = path1) )
  reacdir <- reactive(input$dir)
  output$dirtext <- renderPrint(c(path(),current() ) )
  path1<-"~"
  path <- reactive({
    home <- normalizePath(path1)
    file.path(home, paste(unlist(reacdir()$path[-1]), collapse = .Platform$file.sep))
  })

  current<-reactive({
    a<-sub('.*\\/', '', path() )  
    b<-paste("current subdir:",a)
  })

#  logfilename<- reactive({filename<-paste0(path(),"/",sub('.*\\/', '', path() ),".csv")})
   logfilename <- paste0('logfile',
                         floor(runif(1, 1e+05, 1e+06 - 1)),".txt")
  #    

  logwriter <- observe({
    invalidateLater(1000, session)
    cat(as.character(Sys.time()), '\n', file = logfilename,
        append = TRUE)
  })

  fileReaderData <- reactiveFileReader(500, session,
                                       logfilename, readLines)
 # when using logfilename(): You tried to do something that can only be done from inside a reactive expression or observer.

  # Also not working: fileReaderData <- reactive({file<-reactiveFileReader(500, session,
  #                                       logfilename(), readLines) })

  output$fileReaderText <- renderText({
    text <- fileReaderData()
    length(text) <- 14
    text[is.na(text)] <- ""
    paste(text, collapse = '\n')
  })
}
ui<-fluidPage(
  titlePanel("interactive selection of file and reactive reading"),
  fluidRow(
    column(12,
           shinyDirButton("dir", "1. Choose directory", "Upload")
           ,br(),br(),
            p("This app has a log file which is appended to",
             "every second.")
    )
  ),
  fluidRow(
    column(6, wellPanel(
      verbatimTextOutput("fileReaderText")
    ))
  )
)

shinyApp(ui, server)   

Answer 1

I came to this solution. Tested modifying the mandatory file /folder/folder.csv externally.

library(shiny)
library(shinyFiles)
path1 <- "~"

server <- function(input, output, session) { 
  home <- normalizePath(path1)
  home <- c('home' = home) 

  shinyDirChoose(input, 'dir', roots = home)

  output$dirtext <- renderPrint(current())

  path <- reactive({
    parseDirPath(roots = home, input$dir)
  })

  current <- reactive({
    paste("current subdir:", path())  
  })

  reac <- reactiveValues()

  observeEvent(path(), {
    csv_filename <- paste0(basename(path()), ".csv")

    req(length(file.exists(file.path(path(), csv_filename))) > 0)
    if(file.exists(file.path(path(), csv_filename))) {

      fileReaderData <- reactiveFileReader(1000, session, 
        file.path(path(), csv_filename), 
        read.csv, stringsAsFactors = FALSE)

      reac$df <- fileReaderData()

      output$fileReaderText <- renderText({
        text <- reac$df
        text[is.na(text)] <- ""
        paste(text, collapse = '\n')
      })

    } else {
        "folder_name should have folder_name.csv valid file in it, 2 lines at minimum"
    }
  }) 
}

ui<-fluidPage(
  titlePanel("interactive selection of file and reactive reading"),
  fluidRow(
    column(12,
           shinyDirButton("dir", "1. Choose directory", "Upload")
           ,br(),br(),
           p("shinyapp")
    )
  ),
  fluidRow(
    column(6, wellPanel(
      verbatimTextOutput("fileReaderText"),
      verbatimTextOutput("dirtext")
    ))
  )
)

shinyApp(ui, server)