Question

声明依赖于值而不是另一个变量的最佳方法是什么。这里的想法是，如果值没有改变，它不应该触发进一步的重新计算。例如：

# In the code below we are displaying the result of an input divided by
# ten using integer division.  As a result, many different values result in
# the same value to be displayed and should not trigger re-rendering (ideally)
# However, the obvious implementation using reactive(...) does re-render.
# reactiveValues(...) seems to provide a solution.

library(shiny)

out <- function(...) cat(file = stderr(), ..., "\n")

server <- function(input, output) {

  vals <- reactiveValues()

  tenth <- function() {
    result <- input$n %/% 10
    out('Computing tenth:', input$n, '->', result)
    result
  }

  observeEvent(input$n, { 
    result <- tenth()
    out("Updating vals$tenth:", input$n, '->', result)
    vals$tenth <- result
  })

  output$tenth.val <- renderText({
    result <- vals$tenth
    out("Rendering tenth.val:", result)
    result
  })

  tenth.reactive <- reactive({
    result <- tenth()
    out("Executing tenth.reactive", result)
    result
  })

  output$tenth.ref <- renderText({
    result <- tenth.reactive()
    out("Rendering tenth.ref:", result)
    result
  })
}


ui <- fluidPage(
  sliderInput("n", NULL, min = 0, max = 20, value = 3),
  'One tenth of the above value is',
  tags$ul(
    tags$li(textOutput('tenth.val', inline = T), '(val)'),
    tags$li(textOutput('tenth.ref', inline = T), '(ref)')
  )
)

shinyApp(ui = ui, server = server)

当从9到10滑动时，stderr输出为：

Computing tenth: 9 -> 0 
Updating vals$tenth: 9 -> 0 
Computing tenth: 9 -> 0 
Executing tenth.reactive 0 
Rendering tenth.ref: 0 
Computing tenth: 10 -> 1 
Updating vals$tenth: 10 -> 1 
Computing tenth: 10 -> 1 
Executing tenth.reactive 1 
Rendering tenth.ref: 1 
Rendering tenth.val: 1

请注意Rendering tenth.val只出现一次。即，使用无效值的方法可避免在输出值未更改时重新呈现。但是Rendering tenth.ref出现两次，因为失效级联没有注意到值没有改变。

使用reativeValues()是实现此效果的最佳方法吗？（对我而言似乎有点圆了。）

对值的依赖（不是参考）

0 个答案: