Optimizing Performance - Large File Input in Shiny - r

Question

I have a function (clawCheck) defined in the file CheckClawback.R which takes three data frames as arguments. In my Shiny app, the user uploads three files which are then read into memory and used as the ClawCheck arguments. In order to save time, I want R to start reading a file into memory as soon as it is uploaded, and not only after the "GO" button is pressed, so that once the button is pressed, the arguments for ClawCheck are already in memory and ready to use.
I'm thinking that I have to use eventReactive expressions within the renderTable statement, since I don't want the files to be re-read every time a user changes some input. To avoid further complication, I assume the input is filled in in order, i.e first "account", then "commpaid", then "termriders". When I run the app and the first input file has been uploaded, there is no progress bar appearing which indicates that my code is not working correctly. Here is my (reduced) code:
library('shiny')
source("CheckClawback.R")
ui <- fluidPage(
sidebarLayout(
sidebarPanel(
fileInput("account", "Account File (.csv)"),
fileInput("commpaid", "CommPaid File (.txt)"),
fileInput("termriders", "TermRiders File (.txt)"),
actionButton("do", "GO!")),
mainPanel(
tableOutput("out_table"))
)
)
server <- function(input, output) {
func <- eventReactive(input$do, {
req(acc)
req(comm)
req(term)
datat <<- clawCheck(acc, comm, term)
})
output$out_table <- renderTable({
eventReactive(input$account, {
withProgress(message = "Preparing Account Data...Please Wait", {
acc <<- read.csv(input$account$datapath, header = TRUE, sep = ",")
})
})
eventReactive(input$commpaid, {
withProgress(message = "Preparing CommPaid Data...Please Wait", {
comm <<- read.table(input$commpaid$datapath, header = TRUE, sep = "\t")
})
})
eventReactive(input$termriders, {
withProgress(message = "Preparing TermRiders Data...Please Wait", {
term <<- read.table(input$termriders$datapath, header = TRUE, sep = "\t")
})
})
withProgress(func(), message = "Loading Output...Please Wait")
datat
})
}
shinyApp(ui = ui, server = server)
Ideally, after a file is uploaded, a progress bar should appear, indicating that it is being processed. If, during this process, a second file is uploaded, a second progress bar should appear, indicating that the second file is being processed etc. Once the actual function call happens, I want the input files to be ready to go.
I am very thankful for any help!

Answer 1

Your use of <<- and withProgress() is wrong. Also, using eventReactive() inside a render*() is wrong. I suggest going through RStudio Shiny tutorials to get help on understanding how reactivity works. Also look at showNotification() instead of withProgress(). For now, here's what you probably need -
server <- function(input, output, session) {
acc <- reactive({
validate(need(input$account), "acc not uploaded")
# use showNotification(); use same approach for other files
read.csv(input$account$datapath, header = TRUE, sep = ",")
# use removeNotification() to remove mesg after file is uploaded
})
comm <- reactive({
validate(need(input$commpaid), "comm not uploaded")
read.table(input$commpaid$datapath, header = TRUE, sep = "\t")
})
term <- reactive({
validate(need(input$termriders), "term not uploaded")
read.table(input$termriders$datapath, header = TRUE, sep = "\t")
})
func <- eventReactive(input$do, {
clawCheck(acc(), comm(), term())
})
output$out_table <- renderTable({
func()
})
}