使用反应式表达式

Question

在将任何.csv文件上传到应用程序后，我尝试使用用户选择的变量输入，并绘制一个简单的散点图。

  

错误：不允许从Shinyoutput对象读取对象。

我知道应该在 reactive 函数中添加，但是我不知道在何处添加它。有人可以跟我分享吗？谢谢！

library(shiny)

# Define UI for application that draws a histogram
ui <- fluidPage(

  # Application title
  titlePanel("Javier Test"),

  # Sidebar with a slider input for number of bins 
  sidebarLayout(
    sidebarPanel(

      # Input: Select a file ----
      fileInput("file1", "Choose CSV File",
                multiple = FALSE,
                accept = c("text/csv",
                           "text/comma-separated-values,text/plain",
                           ".csv")),

      # Horizontal line ----
      tags$hr(),

      # Input: Checkbox if file has header ----
      checkboxInput("header", "Header", TRUE),

      # Input: Select separator ----
      radioButtons("sep", "Separator",
                   choices = c(Comma = ",",
                               Semicolon = ";",
                               Tab = "\t"),
                   selected = ","),

      # Input: Select quotes ----
      radioButtons("quote", "Quote",
                   choices = c(None = "",
                               "Double Quote" = '"',
                               "Single Quote" = "'"),
                   selected = '"'),

      # Horizontal line ----
      tags$hr(),

      # Input: Select number of rows to display ----
      radioButtons("disp", "Display",
                   choices = c(Head = "head",
                               All = "all"),
                   selected = "head"),

      #implementing dropdown column 
      uiOutput("input1"), #use this instead when you are trying to upload something instead then process it
      uiOutput("input2"),

      sliderInput("bins",
                  "Number of bins:",
                  min = 1,
                  max = 50,
                  value = 30)
    ),

    # Show a plot of the generated distribution
    mainPanel(
      # Output: Data file ----
      plotOutput("distPlot"),
      plotOutput("scatterplot")
    )
  )
)

library(ggplot2)

# Define server logic required to draw a histogram
server <- function(input, output) {

  #df <- reactiveValues(x= list, y = data.frame())

  output$input1 <- renderUI({
    selectInput("variable", "Variable:",
                colnames(input$file1)) #this will select
  })

  output$input2 <- renderUI({
    selectInput("variable1", "Variable:",
                colnames(input$file1)) #this will select
  })

  # output$distPlot <- renderPlot({
  #   
  #   # obtain input from user for column
  #   x    <- output$contents[, input1$variable] #selecting which column position
  #   
  #   # generate bins based on input$bins from ui.R
  #   bins <- seq(min(x), max(x), length.out = input$bins + 1)
  #   
  #   # draw the histogram with the specified number of bins
  #   hist(x, breaks = bins, col = 'darkgray', border = 'white')
  #   
  # })

  output$scatterplot <- renderPlot({

    x <- output$contents[, input$variable]
    y <- output$contents[, input$variable1]

    #generate plot
    ggplot(output$contents, aes(x=x, y=y, colour=Species)) + geom_point() + theme_classic()

  })

}

shinyApp(ui, server)

更新

我已经开始工作了。解决方法如下。

library(shiny)
library(ggplot2)

# Define UI for application that draws a histogram
ui <- fluidPage(

  # Application title
  titlePanel("Javier Test"),

  # Sidebar with a slider input for number of bins 
  sidebarLayout(
    sidebarPanel(

      # Input: Select a file ----
      fileInput('file1', 'Choose CSV File',
                accept=c('text/csv', 
                         'text/comma-separated-values,text/plain', 
                         '.csv')),

      # Horizontal line ----
      tags$hr(),

      checkboxInput('header', 'Header', TRUE),
      radioButtons('sep', 'Separator',
                   c(Comma=',',
                     Semicolon=';',
                     Tab='\t'),
                   ','),
      radioButtons('quote', 'Quote',
                   c(None='',
                     'Double Quote'='"',
                     'Single Quote'="'"),
                   '"'),

      #implementing dropdown column 
      selectInput('xcol', 'X Variable', ""),
      selectInput('ycol', 'Y Variable', "", selected = "")),

    # Show a plot of the generated distribution
    mainPanel(
      # Output: Data file ----
      plotOutput('MyPlot')
    )
  )
)

# Define server logic required to draw a histogram
server <- shinyServer(function(input, output, session) {
  # added "session" because updateSelectInput requires it


  data <- reactive({ 
    req(input$file1) ## ?req #  require that the input is available

    inFile <- input$file1 

    # tested with a following dataset: write.csv(mtcars, "mtcars.csv")
    # and                              write.csv(iris, "iris.csv")
    df <- read.csv(inFile$datapath, header = input$header, sep = input$sep,
                   quote = input$quote)


    # Update inputs (you could create an observer with both updateSel...)
    # You can also constraint your choices. If you wanted select only numeric
    # variables you could set "choices = sapply(df, is.numeric)"
    # It depends on what do you want to do later on.

    updateSelectInput(session, inputId = 'xcol', label = 'X Variable',
                      choices = names(df), selected = names(df))
    updateSelectInput(session, inputId = 'ycol', label = 'Y Variable',
                      choices = names(df), selected = names(df)[2])

    return(df)
  })

  output$MyPlot <- renderPlot({
    x <- data()[,c(input$xcol, input$ycol)]
    plot(x)
  })
})

shinyApp(ui, server)