Avoid a time-consuming step in a reactive expression in R Shiny

Question

In my Shiny app, users can upload a file which is stored as a reactive dataframe. Inside the reactive expression that is shown below, I call an external time-consuming function (called performDigestion) which requires several seconds to complete.

fastafile_data <- reactive(){
    inFile_fastafile <- input$fastaFile
    req(inFile_fastafile)
    ext <- tools::file_ext(inFile_fastafile$datapath)
    validate(need(ext == "fasta", "Please upload a fasta file"))
    dt.seq <- readAAStringSet(inFile_fastafile$datapath)
    tbl <- performDigestion(dt.seq) ##the time-consuming step
    return(tbl)
  }

Next, I render a Datatable to present the results of the fastafile_data in the UI:

output$dt_fastafile <- DT::renderDataTable({
withProgress(message = 'Computation in progress, this step might take a while. Please wait...', {
  incProgress(1/1)
  fastafile_data()
  })
  }, options = list(scrollX = TRUE, dom = 'lfrtip', pageLength = 10, lengthMenu = c(10, 25, 50, 100)), rownames = FALSE)

In the UI, I also have two additional components (a sliderInput and a numericInput) and in the server-side I handle their values through two observeEvents .

What I would like to achieve is to update the fastafile_data dataframe every time any of these two additional components is triggered without reading the input$fastaFile again and re-running the time consuming performDigestion() function. I would ideally like to trigger the above reactive process again only when a new file is uploaded by the user.

I think the problem here is in my logic and/or there exists a smarter way to do it in ShinyR that I'm currently missing? Can you please point me to the right direction?

EDIT:

When I try to handle the reactive fastafile_data through a second reactive fastafile_data_new the first fastafile_data is re-executed.

fastafile_data_new <- reactive({
    dt <- fastafile_data()
    ##### the condition I'd like to apply
    dt$identifiable <- ifelse(dt$length >= min_peptide_length$choice & dt$length <= max_peptide_length$choice & dt$`mass [Da]` < max_peptide_mass$choice, 1, 0)
    return(dt)
  })