dygraphs series reacting to `date_window`

In this miniapp, the goal is to display raw series and it's average over the selected range:

library(dygraphs)
library(datasets)

server <- function(input, output) {

  reacteddata <- reactive({

    dt = cbind(as.xts(ldeaths),ave=NA)
    if (!is.null(input$dygraph_date_window)){
      start=strftime(input$dygraph_date_window[[1]])
      end=strftime(input$dygraph_date_window[[2]])
      subset = window(as.xts(ldeaths), start=start, end=end)
      ave = rep(mean(subset), length(subset))
      dt[index(as.xts(subset)),"ave"] = ave
      dt = dt[index(as.xts(subset))]
    } else {
      dt[,"ave"] = rep(mean(ldeaths), length(ldeaths))
    }
    dt
  })

  output$dygraph <- renderDygraph({
    dygraph(reacteddata(), main = "Predicted Deaths/Month")
  })
}

ui <- fluidPage(

  sidebarLayout(
    mainPanel(
      dygraphOutput("dygraph")
    )
  )
)

shinyApp(ui = ui, server = server)

It works, even redraws the average line on the zoom ins (using mouse to select zoom date range):

However the catch is that it loses data on each redraw, hence it is impossible to zoom out. Any ideas how to rework it?

It helps to retain full dt dataset outside reactive element and update the ave (average) column based on selected reactive dygraph_date_window. Also, retainDateWindow needs to be set to TRUE.

library(dygraphs); library(shiny); library(datasets); library(xts)

server <- function(input, output) {
  dt = setNames(as.xts(ldeaths), "ldeaths")
  dt = cbind(dt,ave=NA)

  reacteddata <- reactive({
    if (!is.null(input$dygraph_date_window)){
      start=strftime(input$dygraph_date_window[[1]])
      end=strftime(input$dygraph_date_window[[2]])
      subset = window(dt, start=start, end=end)
      ave = rep(mean(subset$ldeaths), nrow(subset))
      dt[index(as.xts(subset)),"ave"] = ave
    } else {
      dt[,"ave"] = rep(mean(ldeaths), length(ldeaths))
    }
    dt
  })

  output$dygraph <- renderDygraph({
    dygraph(reacteddata(), main = "Predicted Deaths/Month") %>% 
      dyOptions(retainDateWindow = TRUE)
  })
}

ui <- fluidPage(
      dygraphOutput("dygraph")
)

shinyApp(ui = ui, server = server)