如何在闪亮中设置默认的 eventReactive 变量？答案

【问题标题】：How to set default eventReactive variables in shiny?如何在闪亮中设置默认的 eventReactive 变量？
【发布时间】：2021-04-26 08:32:33
【问题描述】：

我只想在用户单击操作按钮时更改颜色参数的值，但在 shinyApp 开始时我希望使用默认颜色。

我知道了：

library(shiny)
library(ggplot2)

#data change only once at the begenin
dt <- data.frame(x=runif(100), y=runif(100))


ui <- fluidPage(
  sliderInput("slider1","slider1", value=5, min=1, max=10),
  sliderInput("slider2","slider2", value=0.8, min=0, max=1),
  radioButtons("check1","check1",choices = c("red","blue","green")),
  actionButton("refreshColours","refreshColours"),
  plotOutput("rys")
)



server <- function(input,output){

  col1 <- eventReactive(input$refreshColours,{input$check1}) 

  pp <- reactive({ ggplot(dt, aes(x,y)) + 
      geom_point(size=input$slider1, 
                 alpha=input$slider2, colour=col1()) }) 

  output$rys <- renderPlot({ pp() }) }

shinyApp(ui=ui, server=server)

我只想在shinyApp开始时看到情节，而不是点击操作按钮，所以我需要在开始时“颜色”变量中的默认值。

【问题讨论】：

标签： r shiny

【解决方案1】：

您可以简单地在 ggplot 中为初始状态设置一个默认值：

pp <- reactive({ ggplot(dt, aes(x,y)) + 
      geom_point(size=input$slider1, 
                 alpha=input$slider2, 
                 colour= if(input$refreshColours == 0) "red" else col1() ) 
    })

【讨论】：

【解决方案2】：

除了这里给出的答案，在refreshColors 的数值条件下，您可以在对eventReactive 的调用中设置ignoreNULL = FALSE，并指定selected = "blue"（或您喜欢的任何颜色）对 radioButtons 的调用。

#this is basically the code from the question with the above changes added
library(shiny)
library(ggplot2)

#data change only once at the begenin
dt <- data.frame(x=runif(100), y=runif(100))

ui <- fluidPage(
    sliderInput("point_size","Point Size", value=5, min=1, max=10),
    sliderInput("point_alpha","Point Alpha", value=0.8, min=0, max=1),
    #here is where you select the default value with selected
    radioButtons("point_color","Point Color",choices = c("red","blue","green"),selected = "blue"),
    actionButton("refreshColours","Refresh Colors"),
    plotOutput("plot_out")
)

server <- function(input,output){
#set igoreNULL = FALSE here 
    col1 <- eventReactive( input$refreshColours,{input$point_color},ignoreNULL  = FALSE) 
    
    pp <- reactive({ ggplot(dt, aes(x,y)) + 
            geom_point(size=input$point_size, 
                                 alpha=input$point_alpha, colour=col1()) }) 
    
    output$plot_out <- renderPlot({ pp() }) }

shinyApp(ui=ui, server=server)

您还可以在对 radioButtons 的调用中使用selected = character(0)，这样就不会选择任何单选按钮来启动，并使用一个函数（下面的color_with_default）返回您选择的默认颜色，如果来自radioButtons 为空，因为没有选择时也是如此。该默认颜色用于在应用启动时呈现的初始绘图中，因为在对 eventReactive 的调用中 ignoreNULL 为 false，就像在前面的示例中一样。

library(shiny)
library(ggplot2)

#data change only once at the begenin
dt <- data.frame(x=runif(100), y=runif(100))


ui <- fluidPage(
    sliderInput("point_size","Point Size", value=5, min=1, max=10),
    sliderInput("point_alpha","Point Alpha", value=0.8, min=0, max=1),
    #use selected = character(0) to start with nothing selected
    radioButtons("point_color","Point Color",choices = c("red","blue","green"),selected = character(0)),
    actionButton("refreshColours","Refresh Colors"),
    plotOutput("plot_out")
)



server <- function(input,output){
    #here is the function that returns a default grey color if no button is selected    
    color_with_default <- function( color_in  ){
        if(is.null(color_in)){
            color_in <- "grey"
        } 
        return(color_in)
    }
    
    col1 <- eventReactive(eventExpr =  input$refreshColours, valueExpr = {input$point_color},ignoreNULL = FALSE) 
    
    pp <- reactive({
        ggplot(dt, aes(x,y)) + 
            geom_point(size=input$point_size, 
                                 #the call to the color_with_default function is here
                                 alpha=input$point_alpha, colour= color_with_default(col1()))
    }) 
    
    output$plot_out <- renderPlot({ pp() }) }


shinyApp(ui=ui, server=server)

【讨论】：