r shiny create dropdown menu using folder content - r

Question

This is my day one with R shiny and I'm trying to figure out the following question: assuming that I have a root directory like
/usr/data/
This directory might contain some folders (A,B,C,...) where each folder has contains some files (no folders within them and just files). I am planning to create a dropdown menue based on another dropdown menu. The use select a folder name from the list and the second dropdown menu is automatically loaded with the file names within that folder. For example if folder A is selected and it contains File1 and File2 then the second dropdown will contain those two. This is how I'm doing it right now:
ui.R
library(shiny)
shinyUI(fluidPage(
titlePanel("This is a test app"),
sidebarLayout(
sidebarPanel(
uiOutput("Box1"),
uiOutput("Box2")
),
mainPanel("Display results",
tableOutput("view"))
)
))
server.R
library(shiny)
biz = data.frame(
Folder = c("A", "A", "B" , "B"),
Filename = c("File1","File2","File3","File4"),
stringsAsFactors = FALSE
)
shinyServer(function(input, output) {
output$Box1 = renderUI(selectInput("folder","Select directory",c("None",unique(biz$Folder)),"None"))
output$Box2 = renderUI(
if (is.null(input$folder) || input$folder == "None"){return()
}else selectInput("filename",
"Select dataset",
c("None",unique(biz$Filename[which(biz$Folder == input$folder)])),
"None")
)
subdata1 = reactive(biz[which(biz$Folder == input$folder),])
subdata2 = reactive(subdata1()[which(subdata1()$Filename == input$filename),])
output$view = renderTable({
if(is.null(input$folder) || is.null(input$filename)){return()
} else if (input$folder == "None" || input$filename == "None"){return()
} else return(subdata2())
})
})
As you can see, I'm using a dataframe to take care of that but this should better be dynamic in case that the content of those folders change. So I think the best way is to have list of folder names and then get the contents of that folder and load them in to the second dropdown. I have tried several posts on SO but they are mostly about the content of a csv file and so on. Any help would be much appreciated.
Thanks

Answer 1

I recommend generating UI elements reactively in the following way:
ui.R
library(shiny)
shinyUI(fluidPage(
titlePanel("My Great File Selector"),
fluidRow(
sidebarPanel(
uiOutput("select.folder"),
uiOutput('select.file')
)
)
))
server.R
library(shiny)
shinyServer(function(input, output) {
root <- '~'
output$select.folder <-
renderUI(expr = selectInput(inputId = 'folder.name',
label = 'Folder Name',
choices = list.dirs(path = root,
full.names = FALSE,
recursive = FALSE)))
output$select.file <-
renderUI(expr = selectInput(inputId = 'file.name',
label = 'File Name',
choices = list.files(path = file.path(root,
input$folder.name))))
})
All I have done in ui.R is essentially promise that I will render two UI elements named 'select.folder' and 'select.file' in server.R. That's pretty simple.
In server.R, I specify root, where I want the app to look for directories.
I use renderUI() to generate a UI element in which the user will select the folder and store it in output$select.folder, fulfilling my first promise in ui.R, give it a label of 'Folder Name', and set its choices to the result of list.dirs() (from base R) called with the appropriate arguments. The choice that the user has selected in this UI element will be accessible via input$folder.name because the InputId is 'folder.name'.
I use renderUI() again to generate a UI element that will be used to select a file in that folder and store it in output$select.file, fulfilling my second promise from ui.R. Its choices are based on a call to list.files that uses the folder selected in the first UI element, retrieving it via `input$folder.name'.

Answer 2

You can get the names of the files in a folder with the list.files function.
So something like this should work:
ROOT <- '/usr/data'
dropdown_options <- list.files(paste(ROOT, input$folder, sep = '/'))