Shiny Download File based on File Path - r

Question

I have a file which i generate in shiny
The user clicks a button and the file should download. However nothing happens
The function export_report generates the excel file and saves it to a location. The function then passes back the file location to the download handler so it will download the file. The problem seems to be that it isnt being returned correctly. I have tested the function (export_report) outside of shiny and it returns everything perfectly so I'm clearly doing something wrong from the shiny perspective.
The file itself is created where it is supposed to be on the server because i can download it within RStudio and see it in the file explorer. Can anyone help
# UI Section
downloadButton("downloadRpt", "Download Report")
# Server Section
output$downloadRpt <- downloadHandler(
filename = function() {
mydf <- report()
dateRange <- input$dates_report
selection <- input$selection
myfile <- export_report (mydf, selection, dateRange)
},
content = function(file) {
file.copy(myfile, file)
}
)
I have seen other examples R Shiny: Download existing file which is what my code is based on
EDIT 1: Adding the export_report function with some fake data to run it
export_report <- function(mydf,selection,dateRange) {
# Template for where the template excel file is stored
myoutputTemplate <- '/home/shiny_tutorials/Save to Database/templates/output_template.xlsx'
start_date <- dateRange[1]
end_date <- dateRange[2]
date_range <- paste(start_date ,end_date, sep = " - " )
# Load workbook the template workbook
wb <- loadWorkbook(myoutputTemplate)
# write to the workbook the data frame
writeWorksheet(wb, mydf, sheet="Details",
startRow=8, startCol=2,
header=FALSE)
# add the the customer the user selected
writeWorksheet(wb, selection, sheet="Details",
startRow=3, startCol=3,
header=FALSE)
# date
writeWorksheet(wb, date_range, sheet="Details",
startRow=5, startCol=3,
header=FALSE)
# Create The file Name
filename <- paste(selection, Sys.Date(), sep = " - ") %>%
paste(.,"xlsx", sep = ".")
# removes the % sign and extra qoutes
filename <- gsub (pattern = '\'|%','', x = filename)
# output directory
myoutput <- paste('/home/shiny_tutorials/Save to Database/output/',
filename, sep = '')
# Save workbook
saveWorkbook(wb, myoutput)
# Return File Path
myoutput
}
To call the function you can use the data below
dateRange <- c("2011-09-23","2016-09-23")
selection = "COMPANY_A"
mydf <- iris
myfile <- export_report(mydf,selection,dateRange)
EDIT 2 I have now managed to get an error out of it. When i cat(myfile) in the filename = function() { section of the code i get the error after the correct file path has been returned
Warning in rep(yes, length.out = length(ans)) :
'x' is NULL so the result will be NULL
Warning: Error in ifelse: replacement has length zero
Stack trace (innermost first):
1: runApp
Error : replacement has length zero
This error is basically because my file path does not get passed to the segment myfile so
if someone can tell me how to get the filepath generated by my function to the server section of the code below, that should fix my problem
content = function(file) {
file.copy(myfile, file)
}

Answer 1

Thank you to everyone who commented and clarified my thinking a bit on how the download handler works.
In the end, i created a new function which split up the export function above
The new function i used is called generate_file() which simply returns the file name
generate_file_name <- function(selection) {
# Create The file Name
filename <- paste(selection, Sys.Date(), sep = " - ") %>%
paste(.,"xlsx", sep = ".")
# removes the % sign and extra qoutes
filename <- gsub (pattern = '\'|%','', x = filename)
# output directory
myoutput <- paste('/home/shiny_tutorials/Save to Database/output/',
filename, sep = '')
# Return File Path
myoutput
}
Then in the server side
output$downloadRpt <- downloadHandler(
filename = function() {
selection <- input$company
generate_file_name(selection)
},
content = function(file) {
mydf <- report()
dateRange <- input$dates_report
selection <- input$company
export_report(mydf,selection,dateRange)
myfile <- generate_file_name(selection)
file.copy(myfile, file)
}
)
This then finds the newly created file and exports it for the user

Answer 2

I just checked your problem with this example code and it worked:
output$downloadData <- downloadHandler(
filename = function() {
data <- mtcars
myfile <- "data.csv"
write.csv(data, myfile)
myfile
},
content = function(file) {
print(file) //prints: [...]\\Local\\Temp\\RtmpEBYDXT\\fileab8c003878.csv
file.copy(file, file)
}
)
myfile is the filename of the downloaded file. You cannot use it in file.copy as input, this variable is out of scope. It seems that R creates a temp file name (see the print()).

Answer 3

Try to use the filename function to define your path or a custom file name, and the write.csv in the content part. Example code:
output$downloadData <- downloadHandler(
filename = function() {
paste(<user_name or date for eg>, ".csv", sep="")
},
content = function(file) {
write.csv(data, file)
}
)
I noticed in your comment above, you have asked how the application would generate the correct file when used by multiple users. For this part, you need to use the session.
So if your business logic functions were to come from an R file called foo.R, the server code should look something like:
shinyServer(func = function(input, output, session) {
source("./foo.R", local=TRUE)
......
And this would separate out the session for each user, thereby generating files specific to each, when downloading. Hope this gives you some pointers.