问题描述
我的 Shiny
应用中有一个 selectizeInput
.它处于多选模式,因此用户可以指定多个选择.
I have a selectizeInput
in my Shiny
app. It is in multiple-select mode, so the user can specify more than one selection.
然而,每次添加选择时,依赖于 selectizeInput
的反应都会被触发.假设用户打算选择A
、B
和C
.目前,我的应用程序将对选择 A
、A、B
和 A、B、C
进行昂贵的计算,当只有最后一个是必需的.
However, the reactives that depend on the selectizeInput
get fired every time a selection is added. Suppose that the user intends to select A
, B
and C
. Currently, my app will do it expensive computations for the selections A
, A, B
and A, B, C
, when only the last is required.
我认为解决这个问题的最好方法是将 selectizeInput
的触发延迟一秒左右,让用户有机会输入所有选择.每个新选择都应将计时器设置回 1 秒.我知道 Shiny
提供了一个 invalidateLater
命令,但这会导致反应性地一次又一次地触发.
The best way I can think to solve this is to delay the firing of the selectizeInput
by a second or so to give the user a chance to enter all of the selections. Each new selection should set the timer back to 1 second. I know that Shiny
provides an invalidateLater
command, but this causes the reactive to fire once now and once later.
我怎样才能让反应只在之后触发一次?
How can I get the reactive to only fire once later?
推荐答案
你应该debounce 反应性.
这里有一个 R 实现:https://gist.github.com/jcheng5/6141ea7066e62cafb31c
There is an R implementation here:https://gist.github.com/jcheng5/6141ea7066e62cafb31c
# Returns a reactive that debounces the given expression by the given time in
# milliseconds.
#
# This is not a true debounce in that it will not prevent code{expr} from being
# called many times (in fact it may be called more times than usual), but
# rather, the reactive invalidation signal that is produced by expr is debounced
# instead. This means that this function should be used when code{expr} is
# cheap but the things it will trigger (outputs and reactives that use
# code{expr}) are expensive.
debounce <- function(expr, millis, env = parent.frame(), quoted = FALSE,
domain = getDefaultReactiveDomain()) {
force(millis)
f <- exprToFunction(expr, env, quoted)
label <- sprintf("debounce(%s)", paste(deparse(body(f)), collapse = "
"))
v <- reactiveValues(
trigger = NULL,
when = NULL # the deadline for the timer to fire; NULL if not scheduled
)
# Responsible for tracking when f() changes.
observeEvent(f(), {
# The value changed. Start or reset the timer.
v$when <- Sys.time() + millis/1000
}, ignoreNULL = FALSE)
# This observer is the timer. It rests until v$when elapses, then touches
# v$trigger.
observe({
if (is.null(v$when))
return()
now <- Sys.time()
if (now >= v$when) {
v$trigger <- runif(1)
v$when <- NULL
} else {
invalidateLater((v$when - now) * 1000, domain)
}
})
# This is the actual reactive that is returned to the user. It returns the
# value of f(), but only invalidates/updates when v$trigger is touched.
eventReactive(v$trigger, {
f()
}, ignoreNULL = FALSE)
}
#' @examples
#' library(shiny)
#'
#' ui <- fluidPage(
#' numericInput("val", "Change this rapidly, then pause", 5),
#' textOutput("out")
#' )
#'
#' server <- function(input, output, session) {
#' debounced <- debounce(input$val, 1000)
#' output$out <- renderText(
#' debounced()
#' )
#' }
#'
#' shinyApp(ui, server)
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