Shiny中分配错误的无效（NULL）左侧

Question

我知道这个问题已经发布了几次，但这是我第一次开发我闪亮的东西，我对一些不同的东西感到困惑。其中之一是正确输入数据帧并在输出函数中使用它。

我现在唯一的目标是：

1. 根据用户选择显示头部或完整数据帧

2. 我有一个称为状态的二进制列（状态为通过或失败）。我想按日期分组以计算状态（任何人都可以）并绘制它。

#
# This is a Shiny web application. You can run the application by clicking
# the 'Run App' button above.
#
# Find out more about building applications with Shiny here:
#
#    http://shiny.rstudio.com/
#

library(readxl)
library(shiny)

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

   # Application title
   titlePanel("Data Quality Result Monitoring"),

   # Sidebar with a slider input for number of bins 
   sidebarLayout(
      sidebarPanel(
        fileInput('file1', 'Choose xlsx file',
                  accept = c(".xlsx")
        ),

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

        radioButtons("disp", "Display",
                choices = c(Head = "head",
                            All = "all"),
                selected = "head")

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

         h4("Observations"),
         tableOutput("contents")
      )
)    


# Define server logic required to draw a histogram'
library(ggplot2)
server <- function(input, output) {

   df <- reactive({

     inFile <- input$file1

     if (is.null(inFile))
     return(NULL)

     df <- read_xlsx(inFile$datapath, sheet =  1)

    return(inFile)})

  output$linechart <- renderPlot({
   ndf() <- group_by(df,Execution_Date) %>% summarize( count = n() )

   ggplot(ndf()) + geom_bar(aes(x=week,y=count),stat="identity")
   })

   output$contents <- renderTable({

     # input$file1 will be NULL initially. After the user selects
     # and uploads a file, head of that data file by default,
     # or all rows if selected, will be shown.

     dataset() <- df
     if(input$disp == "head") {
       return(head(dataset()))
     }
     else {
       return(dataset())
     }

   })

}

# Run the application 
shinyApp(ui = ui, server = server)

Answer 1

dataset() <- df

这是你得到错误的地方：

 "Error in <-: invalid (NULL) left side of assignment"

您不能为反应式表达式赋值。反之亦然：

dataset <- df()

使用print 函数来解决这个问题。

您的代码中的另一个错误是：

 df <- read_xlsx(inFile$datapath, sheet =  1)

return(inFile)

你返回了错误的变量，你想返回 df。

下面是适合你的代码：

#
# This is a Shiny web application. You can run the application by clicking
# the 'Run App' button above.
#
# Find out more about building applications with Shiny here:
#
#    http://shiny.rstudio.com/
#

library(readxl)
library(shiny)

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

  # Application title
  titlePanel("Data Quality Result Monitoring"),

  # Sidebar with a slider input for number of bins 
  sidebarLayout(
    sidebarPanel(
      fileInput('file1', 'Choose xlsx file',
                accept = c(".xlsx")
      ),

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

    radioButtons("disp", "Display",
                 choices = c(Head = "head",
                             All = "all"),
                 selected = "head")

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

    h4("Observations"),
    tableOutput("contents")
  )
)    


# Define server logic required to draw a histogram'
library(ggplot2)
server <- function(input, output) {

  df <- reactive({

    inFile <- input$file1

    if (is.null(inFile))
      return(NULL)

    df <- read_xlsx(inFile$datapath, sheet =  1)

    df

    })

  output$linechart <- renderPlot({
    ndf <- group_by(df(),Execution_Date) %>% summarize( count = n() )

    ggplot(ndf + geom_bar(aes(x=week,y=count),stat="identity"))
  })

  output$contents <- renderTable({

    # input$file1 will be NULL initially. After the user selects
    # and uploads a file, head of that data file by default,
    # or all rows if selected, will be shown.

    dataset <- df()
    if(input$disp == "head") {
      return(head(dataset))
    }
    else {
      return(dataset)
    }

  })

}

# Run the application 
shinyApp(ui = ui, server = server)

我还建议您检查代码中的结构和名称。

Answer 2

这是由于ndf() <- group_by(df,Execution_Date) %>% summarize( count = n() )

ndf() 是不存在的 NULL 函数。

df 是一个响应式，您可以将它与df() 一起使用而不是df，这意味着每次响应式更改时都会评估代码。