uploading multiple file input and accessing them through the shiny app to perfrom a loop

Question

I'm pretty stuck here; I have created a simple shiny app with the possibility of uploading multiple files. However, I don't know how can I move on from here and access the files directly within the shiny app, for example, get all the uploaded data files into one data.frame to perform a loop later on.

for example we have 
data_1 <-  "data file 1"
data_2 <-  "data file 2"
data_3 <-  "data file 3"
data_4 <-  "data file 4"

dataSet <- data.frame(DATA= c(1,2,3,4), 
                     DATAFILE=c(data_1 ,data_2 ,data_3 ,data_4))

Is there any way to do that? I hope I have been able to explain myself thoroughly. I really appreciate any help you can provide.

library(shiny)
options(shiny.maxRequestSize = 30 * 1024^2)
ui <- fluidPage(
  fileInput("upload", NULL, buttonLabel = "Upload...", multiple = TRUE),
  tableOutput("files")
)

server <- function(input, output, session) {
  output$files <- renderTable(input$upload)
}
shinyApp(ui, server)

Answer 1

input$upload is a data.frame containing four columns, to read the files we'll need datapath column that contains the temp path with the uploaded data, in this case they are csv's. From there we use a function like readr::read_csv() to transform the raw uploaded data into a df.

We can construct a reactive that consists in a list with all the uploaded files in it.

  # read all the uploaded files
  all_files <- reactive({
    req(input$upload)
    purrr::map(input$upload$datapath, read_csv) %>%
      purrr::set_names(input$upload$name)
  })

Full app:

library(shiny)
library(tidyverse)
library(DT)


# create some data to upload
write_csv(mtcars, "mtcars.csv")
write_csv(mpg, "mpg.csv")
write_csv(iris, "iris.csv")

options(shiny.maxRequestSize = 30 * 1024^2)

ui <- fluidPage(
  fileInput("upload", NULL, buttonLabel = "Upload...", multiple = TRUE),
  DT::DTOutput("files"),
  tableOutput("selected_file_table")
)

server <- function(input, output, session) {
  output$files <- DT::renderDT({
    DT::datatable(input$upload, selection = c("single"))
  })

  # read all the uploaded files
  all_files <- reactive({
    req(input$upload)
    purrr::map(input$upload$datapath, read_csv) %>%
      purrr::set_names(input$upload$name)
  })
  
  #select a row in DT files and display the corresponding table
  output$selected_file_table <- renderTable({
    req(input$upload)
    req(input$files_rows_selected)

    all_files()[[
    input$upload$name[[input$files_rows_selected]]
    ]]
  })
}

shinyApp(ui, server)

Answer 2

There are two stages to this:

When you select a file what happens is that is gets copied into a temp directory. One of the values returned by the input is the location of the temp file, another is the original file name.

Once you have the file path you can use a function to read the data from that temp file.

The example at the bottom of this should be helpful (although your example needs a little bit more than this one because you have selected multiple files):

https://shiny.rstudio.com/reference/shiny/1.6.0/fileInput.html