Issues while updating cell in R shiny datatable

[snt]

I am trying to add an editable datatable in r shiny. I have two components to it. First being allowing the user to add a new row and delete a selected row. Secondly when the user changes any value in the cell it should update the corresponding cell. The issue I am facing is if the user edits column dd it should update the value for column ff based on the formula. Also when I edit a cell and add new rows the new columns come up as blanks. How can I fix this.Thank you.

### Libraries
library(shiny)
library(dplyr)
library(DT)

### Data
input_data <- data.frame(aa = c("Brand1", "Brand2","Brand3"),
                         bb = c(2000, 3000, 4000),
                         cc = c (.5, .5, .5),
                         dd = c(2000, 3000, 4000),
                         ee = c (.5, .5, .5),
                         ff = c (.5, .5, .5),
                         gg = c (.5, .5, .5),
                         stringsAsFactors = FALSE)

### Shiny App
shinyApp(
  ui = basicPage(
    mainPanel(
      
      actionButton("reset", "Reset"),
      actionButton("add_btn", "Add"),
      actionButton("delete_btn", "Delete"),
      tags$hr(),
      DT::dataTableOutput("mod_table")    )
  ),
  server = function(input, output) {
    
    #demodata<-input_data
    
    this_table <- reactiveVal(input_data)
    
    observeEvent(input$add_btn, {
      t = rbind(data.frame(aa = "default",
                           bb = 1000000,cc = 2.0,dd = 20000, ee = 40,ff = 00 , gg = 00), this_table())
      this_table(t)
    })
    
    observeEvent(input$delete_btn, {
      t = this_table()
      print(nrow(t))
      if (!is.null(input$shiny_table_rows_selected)) {
        t <- t[-as.numeric(input$shiny_table_rows_selected),]
      }
      this_table(t)
    })
    
    
     observeEvent(input$mod_table_cell_edit, {
       v <- this_table()
      # #
      proxy = dataTableProxy("mod_table")
       print(names(v$data))
       info = input$mod_table_cell_edit
       str(info)
       i = info$row
       j = info$col
       k = info$value
       str(info)
    # #
       isolate(
         if (j %in% match(c("aa","bb","cc","dd","ee","ff","gg"), names(v$data))) {
        #   print(match(c("ratio","cost", "updated_price"), names(v$data)))
           v$data[i, j] <<- DT::coerceValue(k, v$data[i, j])
           print(v$data)
    # #
    # #
           if (j %in% match("reach_percentage", names(v$data))) {
             v$data$ff <<- v$data$dd / 10000
           }
         } else {
           stop("You are not supposed to change this column.") # check to stop the user from editing only few columns
         }
       )
       replaceData(proxy, v$data, resetPaging = FALSE)  # replaces data displayed by the updated table
     })
    # 
     observeEvent(input$reset, {
       this_table <- input_data # your default data
     })
    # #
    
    output$mod_table <- DT::renderDataTable({
      datatable(this_table(), selection = 'single',editable = TRUE, options = list(dom = 't'))
      
    })
    
    
  }
)