dependencies in shiny objects - r

Question

In my app, the user needs to pick a folder, and in that folder he needs to pick a file (the suffix of the file name is '.seg')
This code is working-
library(shiny)
ui <- shinyUI(fluidPage(
# select a folder
column(2, absolutePanel(fixed = TRUE, width = '180px',
selectInput("pick_a_folder", label = '', selected='choose a folder',
choices = setNames(as.list(c('choose a folder',
basename(list.dirs(recursive = FALSE)))),
c('choose a folder',
basename(list.dirs(recursive = FALSE))))))),
# select a file
column(2, absolutePanel(fixed = TRUE, width = '180px',
conditionalPanel(condition='!(input.pick_a_folder=="choose a folder")',
uiOutput('fileselection'))))
))
server <- shinyServer(function(input, output) {
# dinamic file selection. find the files list after folder is choosen
output$fileselection <- renderUI({
selectInput('pick_file', '', selected = 'choose a file',
choices=setNames(as.list(c('choose a file',basename(list.files(path=input$pick_a_folder,recursive=FALSE, pattern='\\.seg$')))),
c('choose a file',basename(list.files(path = input$pick_a_folder, recursive = FALSE, pattern='\\.seg$')))))
})
})
shinyApp(ui = ui, server = server)
The issue is that if I add a folder to the working directory after I ran the code, it will not appear.
So I tried to move the folder selection to the server, and make it dependent on a refresh button, but I get an error
Error in list.files: invalid 'path' argument
this is my code-
library(shiny)
ui <- shinyUI(fluidPage(
# refresh butten for root directory
column(1, absolutePanel(fixed=TRUE, actionButton("refresh_wd", "refresh"))),
# select a folder
column(2, absolutePanel(fixed = TRUE, width = '180px', uiOutput('folderselection'))),
# select a file
column(2, absolutePanel(fixed = TRUE, width = '180px',
conditionalPanel(condition='!(input.pick_a_folder=="choose a folder")',
uiOutput('fileselection'))))
))
server <- shinyServer(function(input, output) {
# refresh root directory
wd_folders <- eventReactive(input$refresh_wd, {
basename(list.dirs(recursive = FALSE))
})
output$folderselection <- renderUI({
selectInput('pick_a_folder', '', selected = 'choose a folder',
choices = setNames(as.list(c('choose a folder', wd_folders())),
c('choose a folder', wd_folders())))
})
# dinamic file selection. find the file list after folder is choosen
output$fileselection <- renderUI({
selectInput('pick_a_file', '', selected = 'choose a file',
choices=setNames(as.list(c('choose a file',basename(list.files(path=input$pick_a_folder,recursive=FALSE, pattern='\\.seg$')))),
c('choose a file',basename(list.files(path = input$pick_a_folder, recursive = FALSE, pattern='\\.seg$')))))
})
})
shinyApp(ui = ui, server = server)
Any help would be appreciated

Answer 1

Because you use eventReactive() the list of folders and even the folder selection will only be displayed after somebody clicked on the 'Refresh' button. You can avoid this by using ignoreNULL = FALSE :
wd_folders <- eventReactive(input$refresh_wd, {
basename(list.dirs(recursive = FALSE))
}, ignoreNULL = FALSE)
If you don't do this, the value of wd_folders() will be NULL to start with, so your condition for your conditionalPanel is fulfilled (it's not "select a folder") and hence your app tries to read the files in directory NULL. This gives you your error.
If you want to be extra safe, you can add validate(need()) to the UI rendering as well, eg:
output$fileselection <- renderUI({
validate(need(input$pick_a_folder, label = "Pick a folder first"))
validate(need(dir.exists(input$pick_a_folder),
label = "Something went wrong. Contact me."))
selectInput('pick_a_file', '', selected = 'choose a file',
...)
})
This isn't necessary to fix your problem, but I find it good practice in Shiny.

Answer 2

Here is a minimal example that auto refresh the folders every 5 seconds.
It does still produce an initial warning about path being invalid for the reasons #JoriMeys explained.
library(shiny)
ui <- shinyUI(fluidPage(
column(1,
absolutePanel(fixed=TRUE,
textOutput('wd'),
uiOutput('folderselection'),
conditionalPanel(
condition='!(input.pick_a_folder=="choose a folder")',
uiOutput('fileselection'))
)
)
)
)
server <- shinyServer(function(input, output) {
output$wd <- renderText(basename(
list.files(path = input$pick_a_folder,
recursive=FALSE)
)
)
button <- reactiveTimer(intervalMs = 5000)
# refresh root directory
wd_folders <- reactive({
button()
basename(list.dirs(recursive = FALSE))
})
output$folderselection <- renderUI({
selectInput('pick_a_folder', '',
choices = c('choose a folder', wd_folders()
)
)
})
# dinamic file selection. find the file list after folder is choosen
output$fileselection <- renderUI({
selectInput('pick_a_file', '',
selected = 'choose a file',
choices=c('choose a file',
basename(list.files(path = input$pick_a_folder,recursive=FALSE))))
})
})
shinyApp(ui = ui, server = server)