How to run an R script when the shiny app is running with click of a button?

Question

My requirement is to run a script from shiny app whenever a button is clicked and show the results in the UI after the script run.

I tried the below inside the server but the UI shows the updated results only if I reload the app.

source("recalculate.R", local = TRUE)

And the below is not working at all.

observeEvent(input$recalculatebtn, source("recalculate.R", local = TRUE))

Can anyone please help me to sort this out?

Adding the below a very basic sample case.

Data:

TableA = data.frame(A = c(1:3), B = c(4:6))

Recalculate.R:

TableC = data.frame(C = TableA$A * TableA$B)

UI:

ui = shinyUI(
  fluidPage(
    
    
      sidebarPanel(
                    conditionalPanel(condition = "input.tabselected == 'tab1'", actionButton("recalcbtn", "Recalculate"))
                  ),
    mainPanel(uiOutput("mainpanel"))
    )
  )

Server:

 server = function(input, output, session) {
   
    output$mainpanel = renderUI({
      
      tabsetPanel(
        tabPanel("ModifyTableA", value = 'tab1', rHandsontableOutput("OTableA")),
        tabPanel("UpdatedValues", value = 'tab2', DT::dataTableOutput("OTableC")),
        id ="tabselected"
      )
      
    })
     
    
    indat <- reactiveValues(data=TableA)
    
    output$OTableA = 
      renderRHandsontable({
        indat$data <- TableA
        rhandsontable(indat$data)
      })
    
    output$OTableC = DT::renderDataTable(TableC)
    
    observeEvent(input$recalcbtn,  

{
TableA <<- input$OTableA
source("Recalculate.R", local = TRUE))
}
    
  }

Answer 1

Hereafter a simplified example of using a reactiveVal .
I didn't go into the specifics of handsontable which would be another question, but input$OTableA won't work as such because it returns a full table object and not only the data.

library(rhandsontable)
TableA = data.frame(A = c(1:3), B = c(4:6))
TableC = data.frame(C = TableA$A )

library(shiny)
ui = shinyUI(
  fluidPage(


    sidebarPanel(
      conditionalPanel(condition = "input.tabselected == 'tab1'", actionButton("recalcbtn", "Recalculate"))
    ),
    mainPanel(uiOutput("mainpanel"))
  )
)

server = function(input, output, session) {

  output$mainpanel = renderUI({

    tabsetPanel(
      tabPanel("ModifyTableA", value = 'tab1', rHandsontableOutput("OTableA")),
      tabPanel("UpdatedValues", value = 'tab2', DT::dataTableOutput("OTableC")),
      id ="tabselected"
    )

  })

  TableC_react <- reactiveVal(TableC)
  indat <- reactiveValues(data=TableA)

  output$OTableA =
    renderRHandsontable({
      indat$data <- TableA
      rhandsontable(indat$data)
    })

  output$OTableC = DT::renderDataTable(TableC_react())

  observeEvent(input$recalcbtn,

               {

                 #source("Recalculate.R", local = TRUE)
                 result <- TableC_react()+1 # could be the result of Recalculate
                 TableC_react(result)
  })

}

shinyApp(ui=ui,server)