R shiny: How to get an reactive data frame updated each time pressing an actionButton without creating a new reactive data frame?

Question

My shiny app allows user to upload a csv by using fileInput and stored as an reactive object df_data. I then created a numericInput for user to enter a row

Answer 1

Below is a working solution. I created a reactiveValues to store the dataframe. When a file is chosen, the dataframe gets populated. When the delete button is pressed, that same dataframe gets a row deleted. The table always outputs whatever that dataframe object is holding. I hope this code can be a good learning material

runApp(shinyApp(
ui=(fluidPage(
  titlePanel("amend data frame"),

  mainPanel(
    fileInput("file", "Upload file"),

    numericInput("Delete", "Delete row:", 1, step = 1),
    actionButton("Go", "Delete!"),

    tableOutput("df_data_out")
  )
)),
server = (function(input, output) {
  values <- reactiveValues(df_data = NULL)

  observeEvent(input$file, {
    values$df_data <- read.csv(input$file$datapath)
  })

  observeEvent(input$Go, {
    temp <- values$df_data[-input$Delete, ]
    values$df_data <- temp

  })

  output$df_data_out <- renderTable(values$df_data)
})))