Update input before ReactiveFlush

[aha-incom]

Hi.

I've tried creating a reprex of my original issue. Basically I would like to find out if it is possible to force the observeEvent to trigger before triggering the calculation of out$table ?

library(shiny)
ui <- fluidPage(
  shiny::selectInput("nrows",
                     "Select nrows",
                     choices = 1:10),
  shiny::selectInput("ncols",
                     "Select ncols",
                     choices = 1:11,
                     selected = 11),
 
  tableOutput("table")
)

server <- function(input, output, session) {
  
  observeEvent(input$ncols, {
    updateSelectInput(session,
                      "nrows",
                      selected = 1)
  })
  
  output$table <- renderTable({
    Sys.sleep(2)
    mtcars[1:as.numeric(input$nrows), 1:as.numeric(input$ncols)]
  })
  
}

shinyApp(ui, server)

I have a similar but more complex App where I want to update a selectInput based on another Input. However the output should still be a reactive on both.

Is this simply bad design by me? Thanks in advance

[cpsievert]

It's not entirely clear to me what your intention is, but it seems you want something similar to this?

library(shiny)
ui <- fluidPage(
  shiny::selectInput("nrows",
    "Select nrows",
    choices = 1:10),
  shiny::selectInput("ncols",
    "Select ncols",
    choices = 1:11,
    selected = 11),
  
  tableOutput("table")
)

server <- function(input, output, session) {
  
  observeEvent(input$ncols, {
    freezeReactiveValue(input, "nrows")
    updateSelectInput(session, "nrows", selected = 1)
  })
  
  output$table <- renderTable({
    mtcars[seq_len(input$nrows), seq_len(input$ncols)]
  })
  
}

shinyApp(ui, server)

Note also, that observers like observeEvent() do have a priority argument to make sure they execute before/after other observers/render functions, but using that is usually an indication that you may want to structure your reactive logic differently