How to run batch processing in Shiny

I have an Excel file with several tabs. How can I run my shiny App looping through the tabs -- using one tab (one at a time) as input?

Here is a simple example. In reality, raw_input is the Excel file with 3 tabs. In this code, out3() will only be run for tab1.

Final outcome I am looking for is Output.csv with 3 tabs:

  1. Tab1 is out3() calculated using tab1
  2. Tab2 is out3() calculated using tab2
  3. Tab3 is out3() calculated using tab3
library(shiny)

ui <- fluidPage(
  shiny::downloadButton('download_button', "Save")
)

server <- function(input, output, session) {
  
raw_input <- reactive({
  df <- data.frame(tab1 = c(1, 2, 3), 
                   tab2 = c(4, 5, 6), 
                   tab3 = c(1, 1, 1)
})

# IN THIS EXAMPLE BELOW, IT ONLY RUNS FOR THE 1ST TAB
# I NEED TO RUN IT FOR EACH TAB

out1 <- reactive({
  return(raw_input()[[1]]**2)
})

out2 <- reactive({
  return(out1() * 5)
})

out3 <- reactive({
  return(out1()+out2())
})

output$download_button <- shiny::downloadHandler(
  filename = function() {paste("Output.csv")},
  content  = function(file) {
    write.csv(out3(), file)
  }
)
}

shinyApp(ui, server)

Do you need the results ouf out1 and out2 somewhere else or is this just to create out3.
In this case you can combine everything, instead creating a chain of reactives.

out3 <- reactive({
  out1 = raw_input()[[1]]**2
  out2= out1 * 5
  out3=  out1+out2
  return(out3)
})

then you can repeat this for the 3 tabs:

out3_tab1 <- reactive({
  out1 = raw_input()[[1]]**2
  out2= out1 * 5
  out3=  out1+out2
  return(out3)
})

out3_tab2 <- reactive({
  out1 = raw_input()[[2]]**2
  out2= out1 * 5
  out3=  out1+out2
  return(out3)
})

As this would be an unnecessary duplication of code, better write this into a function that can be used multiple times.

calculate_out3 = function(data, tab {
  out1 = data[[tab]]**2
  out2= out1 * 5
  out3=  out1+out2
  return(out3)
}

and call this in the reactive environment:

out3_tab1 = reactive({
 calculate_out3(raw_input(), 1) 
})

out3_tab2 = reactive({
 calculate_out3(raw_input(), 2) 
})

Something like that.
But with this solution your need to have 3 download buttons as well, one for each output.

In reality, the reactive objects have complex calculations and are use elsewhere (by many other functions/reactive objects).

Thank you for your input. If you / anyone have other suggestions, let me know. Thanks so much!