Downloading the outputs of a reactive table in R shiny - r

Question

I have an R shiny app that gets a .csv import from a user and searches the imported data across a built-in data frame, then gives the % match in the output. The UI is very simple, with a few different inputs (import .csv, a slider, and some radio buttons). What I want is to be able to take the reactive table output and print this to a .csv that the user can download to their machine. The server side of the app looks something like this:
server <- function(input, output){
rvals <- reactiveValues()
observeEvent(input$file_1,{
req(input$file_1)
rvals$csv <<- read.csv(input$file_1$datapath, header = TRUE)
#some data processing here
})
output$contents <- renderTable({
if(input$select == 1){
x <- function
}else if(input$select == 2){
x <- function
}else if(input$select == 3){x <- function}
#some more data processing and formatting here
return(x)
},digits = 4)
}
I would like to have the data table x be able to become a .csv that can be downloaded by clicking a download button. In the server, I added the following code, but when I try to download the data it just downloads a blank file and says "SERVER ERROR" in my downloads manager on my machine.
output$downloadData <- downloadHandler(
filename = "thename.csv",
content = function(file){
write.csv(x, file)
}
In the console I also get the error message:
Warning: Error in is.data.frame: object 'x' not found [No stack trace available]

Answer 1

The object you create inside the expression of renderTable is not available outside of it. Instead you could assign it to the reactive values you set up. Below is a working example (note that I have tried to replicate your code so the data will not be available until you click on "Upload CSV", which here just calls mtcars).
library(shiny)
ui = fluidPage(
sidebarPanel(
actionButton(inputId = "uploadCsv", label = "Upload CSV:", icon = icon("upload")),
selectInput(inputId = "preProc", label = "Pre-processing", choices = c("Mean"=1,"Sum"=2)),
downloadButton("downloadData", label = "Download table")
),
mainPanel(
h4("My table:"),
tableOutput("contents")
)
)
server <- function(input, output) {
rvals <- reactiveValues(
csv=NULL,
x=NULL
)
observeEvent(input$uploadCsv,{
rvals$csv <- mtcars # using example data since I don't have your .csv
# rvals$csv <- read.csv(input$file_1$datapath, header = TRUE)
#some data processing here
})
output$contents <- renderTable({
# Assuing the below are functions applied to your data
req(
input$preProc,
!is.null(rvals$csv)
)
if(input$preProc == 1){
rvals$x <- data.frame(t(colMeans(mtcars)))
}else {
rvals$x <- data.frame(t(colSums(mtcars)))
}
return(rvals$x)
},digits = 4)
output$downloadData <- downloadHandler(
filename = "myFile.csv",
content = function(file){
write.csv(rvals$x, file)
}
)
}
shinyApp(ui,server)

Answer 2

EventReactive already outputs a reactive value, you don't need to create an extra reactiveVal, see example below :
library(shiny)
# Define UI
ui <- fluidPage(
# Application title
titlePanel("Test"),
mainPanel(
actionButton("show", "Download"),
textOutput("result")
)
)
server <- function(input, output) {
csvfile <- eventReactive(req(input$show), ignoreNULL = T, {
"Content of file"
})
output$result <- reactive(
paste("result : ",csvfile()))
}
# Run the application
shinyApp(ui = ui, server = server)
I would also avoid to use <<-operator in a reactive expression.