check existence of reactive in shiny - r

Question

I have a shiny app where you can upload some raw data and build a summarizedExperiment (let's call it RAW) or you can upload an already processed summarizedExperiment (let's call it FINAL). Now I need to save in a reactive object RAW or FINAL. I tried something like this:
sumexp_all = reactive({
if(!is.null(RAW())){
list(sumexp_data = RAW()$sumexp_data, sumexp_data_mean = RAW()$sumexp_data_mean, replicates = RAW()$replicates)
}else if(!is.null(input$finalsumexpinput)){
readRDS(file = input$finalsumexpinput$datapath)
}else{
NULL
}
})
But in this case it works only if I have RAW (if I don't have RAW (so should be NULL since there are many req() in the pipeline) and I want to upload FINAL, nothing happens). If reverse the if conditions (before FINAL and then RAW) I can upload the FINAL. What's wrong? Is it correct to evaluate a reactive with is.null()?
I tried something else like this:
sumexp_all = reactive({
checkerror <- tryCatch(RAW(), error = function(e) "empty")
if(checkerror != "empty"){
list(sumexp_data = RAW()$sumexp_data, sumexp_data_mean = RAW()$sumexp_data_mean, replicates = RAW()$replicates)
}else if(!is.null(input$finalsumexpinput)){
readRDS(file = input$finalsumexpinput$datapath)
}else{
NULL
}
})
But the shiny app crashes and returns this error:
Warning: Error in if: argument is of length zero
And that's weird because if I print checkerror it correctly returns "empty" if's empty.
UPDATE:
I made some testing in order to find where is the problem, and the problem is with the RAW() reactive. Basically I tried this code to find the problem:
checkraw = reactive({
if(is.null(RAW())){
"raw is null"
}else{
"raw is not null"
}
})
checkinp = reactive({
if(is.null(input$finalsumexpinput$datapath)){
"input non loaded"
}else{
"input loaded"
}
})
output$printcheck= renderPrint({
paste(checkraw(), ",", checkinp())
})
So what I expect from this code is that if RAW() doesn't exist and I uplaod the rds file, it' printed "raw is null, input loaded", but what happens is that nothing is displayed.
If RAW() exists then it's correctly printed "raw is not null, input not loaded"
Then I tried to print only checkinp() (removing the checkraw() reactive) and then checkinp() is correctly printed.
So it seems to me that the problem is in the evaluation of the RAW() reactive. Do you think that the problem could be that RAW() depends on others reactive variables (so there is a req() inside it).
EDIT:
Here is a reproducible example.
ui <- shinyUI(pageWithSidebar(
headerPanel("check"),
sidebarPanel(
actionButton("Button", "enable raw"),
textInput("text", "write something", "something..."),
br(),
),
mainPanel(
verbatimTextOutput("printcheck"),
verbatimTextOutput("checkfin")
)
))
server <- shinyServer(function(input, output) {
stepa = eventReactive(input$Button, {
rnorm(100)
})
stepb = reactive({
req(stepa())
stepa() * 100
})
output$printcheck = renderPrint({
is.null(stepb())
})
fin = reactive({
if(!is.null(stepb())){
stepb()
}else{input$text}
})
output$checkfin = renderPrint({
fin()
})
})
shinyApp(ui=ui,server=server)
As you can see output$checkfin is printed ONLY if stepb() is not null even if in this case should be printed input$text

Answer 1

I posted the problem on the shiny github page. For those interested, here's the answer.
https://github.com/rstudio/shiny/issues/3533