I have a data.table with following four columns:

col1 = as.numeric(0),
col2 = as.numeric(0),
col3 = as.numeric(0),
col4 = as.numeric(0)

In case of !is.na(df$col2) OR df$col2 != 0
col4 = col2 + col3
otherwise
col4 = col1 + col3

In frames of a shiny app I have used a nested ifelse() statement to do this conditional calculation. In this regard I have tried the following two versions of code but col4 is not getting a result in either of cases.

Can someone show me a right approach?

I went through several SO questions but could not effectively figure out how to use their solutions in my case. If there is a similar question in this forum with a relevant solution then I would get it and discard my own question.

      #The 1st version of my code:

      library(shiny)
      library(shinydashboard)
      library(rhandsontable)
      library(data.table)

      DF <- data.table(
               col1 = as.numeric(0),
               col2 = as.numeric(0),
               col3 = as.numeric(0),
               col4 = as.numeric(0),
               stringsAsFactors = FALSE
          )

      ui <- fluidPage(
        dashboardPage(
          dashboardHeader(),
          dashboardSidebar(        
            menuItem("Calculation", tabName = "calc")
          ),
          dashboardBody(
            tabItems(
              tabItem(tabName = "calc",
                      rHandsontableOutput("table")
              )
            )
          )
        )
      )

      server = function(input, output, session) {

        data <- reactiveValues()
 
        observe({ data$df <- as.data.table(DF) })

        observeEvent(input$table, {
          data$df[[4]] <- ifelse(
                        !is.na(data$df[[2]]) | data$df[[2]] != 0,
                        data$df[[2]] + data$df[[3]],
                        ifelse(
                          data$df[[2]]==NA | data$df[[2]] == 0,
                          data$df[[1]] + data$df[[3]],
                          NULL
              )
           )
        })

        output$table <- renderRHandsontable({
          rhandsontable(data$df)
        })
      }

      shinyApp(ui, server)


    `#The 2nd version of mycode:`


      library(shiny)
      library(shinydashboard)
      library(rhandsontable)
      library(data.table)


      DF <- data.table(
               col1 = as.numeric(0),
               col2 = as.numeric(0),
               col3 = as.numeric(0),
               col4 = as.numeric(0),
               stringsAsFactors = FALSE
            )

      ui <- fluidPage(
        dashboardPage(
          dashboardHeader(),
          dashboardSidebar(        
            menuItem("Calculation", tabName = "calc")
          ),
          dashboardBody(
            tabItems(
              tabItem(tabName = "calc",
                  rHandsontableOutput("table")
              )
            )
          )
        )
      )

      server = function(input, output, session) {

        data <- reactiveValues()

        observe({ data$df <- as.data.table(DF) })

        output$table <- renderRHandsontable({
          data$df[, col4 := ifelse(!is.na(data$df[[2]]) | data$df[[2]] != 0,
                           data$df[[2]] + data$df[[3]],
                             ifelse(data$df[[2]]== NA | data$df[[2]] == 0,
                                    data$df[[1]] + data$df[[3]],
                                    NULL))]
          rhandsontable(data$df)
        })
      }

      shinyApp(ui, server)