R Shiny：eventReactive输出的初始呈现

Question

What I'm trying to achieve is to have an initial table to be rendered right as the app is executed. But then, update the table only on executing action.

Here's the example:

library(shiny)
library(data.table)

dt <- data.table(x = c("a", "b"), y = c(0,0))

ui <- fluidPage(

  sidebarLayout(

    sidebarPanel(
      selectInput(inputId = "inSelect", 
                  label = "Select:", 
                  choices = dt[,unique(x)]), 

      actionButton(inputId = "trigger",
                   label = "Trigger", 
                   icon = icon("refresh"))
    ),

    mainPanel(
      tableOutput("outTable")
    )

  )

)



server <- function(input, output){

  re <- eventReactive(input$trigger, {
    dt[x == input$inSelect, y := y + 1]
  })

  output$outTable <- renderTable({
    re()
  })

}

shinyApp(ui, server)

So the issue is that under renderTable() I can put either dt to show initial table or re() to show each update after first press of the "Trigger" button.

Answer 1

Do

  re <- eventReactive(input$trigger, {
    dt[x == input$inSelect, y := y + 1]
  }, ignoreNULL = FALSE)

From ?eventReactive :

Both observeEvent and eventReactive take an ignoreNULL parameter that affects behavior when the eventExpr evaluates to NULL (or in the special case of an actionButton, 0).