R：在数据处于活动状态时使用变量

Question

I am trying to use variables created under data reactive(). Following is my code. It's a ready to use example

UI

 library(shiny)
 shinyUI(fluidPage(
titlePanel("Old Data"),

# Sidebar with a slider input for number of bins
sidebarLayout(
sidebarPanel(
  selectInput("var",
              label = "Choose a Group to Display",
              choices = c("4", "6","8"),
              selected = "4")
),

# Show a plot of the generated distribution
mainPanel(
  plotOutput("Plot1"),
  plotOutput("Plot2")
)
)
))

SERVER

library(shiny)
library(datasets)
library(ggplot2)
cars=mtcars

shinyServer(function(input, output) {

data_rec =reactive({     
d=cars[cars$cyl==input$var,] 
d1=d[d$am==0,]
list(d=d,d1=d1)
})

output$Plot1 <- renderPlot({
data2=data_rec()
ggplot(data2$d,aes(x=gear,y=wt))+geom_boxplot() })

output$Plot2 <- renderPlot({   
ggplot(data2$d1,aes(x=gear,y=wt))+geom_boxplot() })  
 })

I am only able to create 1 chart for the other I am receiving an Error: object 'data2' not found. Help me with defining variables inside data reactive and then using them to plot.

Answer 1

I think there is some confusion as to how variables are scoped here. data2 is not defined in the output$plot2 code block, and it shares no definitions with those defined in the output$plot1 code block.

I think this does what you want, although I would have used a reactiveValues for data_rec .

library(shiny)
library(datasets)
library(ggplot2)

u <- shinyUI(fluidPage(
  titlePanel("Old Data"),

  # Sidebar with a slider input for number of bins
  sidebarLayout(
    sidebarPanel(
      selectInput("var",
                  label = "Choose a Group to Display",
                  choices = c("4", "6","8"),
                  selected = "4")
    ),

    # Show a plot of the generated distribution
    mainPanel(
      plotOutput("Plot1"),
      plotOutput("Plot2")
    )
  )
))


cars=mtcars

s <- shinyServer(function(input, output) {

  data_rec =reactive({     
    req(input$var)
    d=cars[cars$cyl==input$var,] 
    d1=d[d$am==0,]
    list(d=d,d1=d1)
  })

  output$Plot1 <- renderPlot({
    data2=data_rec()
    ggplot(data2$d,aes(x=gear,y=wt))+geom_boxplot() 
    })

  output$Plot2 <- renderPlot({  
   data2=data_rec()
  ggplot(data2$d1,aes(x=gear,y=wt))+geom_boxplot() 
  })  
})
shinyApp(u,s)

yielding:

Answer 2

You forgot to create your data in output$Plot2 .

It should look like this:

output$Plot2 <- renderPlot({ 
                data2 <- data1()
                data2$d1 %>% 
                  ggplot + 
                  aes(x = gear,y = wt) + 
                  geom_boxplot() 
})  

You could also put the reactive parts directly in the renderPlot functions and avoid having lists to work with ggplot...

The server part would look like this:

server <- shinyServer(function(input, output) {
          output$Plot1 <- renderPlot({

             data %>% 
               filter(cyl == input$var) %>% 
                 ggplot + 
                 aes(x = gear, y = wt) + 
                 geom_boxplot()
          })

         output$Plot2 <- renderPlot({ 

            data %>% 
              filter(cyl == input$var & am == 0) %>% 
                ggplot + 
                aes(x = gear,y = wt) + 
                geom_boxplot()
          })  
})