R 从反应式表达式中的不同数据帧中减去列

新手来到这里，希望得到一些指导

我正在尝试构建一个简单的闪亮应用程序，允许用户上传两个csv文件，从一个数据帧（B）中减去另一个（a）[都具有相同的列结构]，并将这些结果合并到df a的相应列中。然后，它应该在UI中显示此更新数据帧的结果

当我尝试运行应用程序时，它出现以下错误：

Error in .getReactiveEnvironment()$currentContext() : 
  Operation not allowed without an active reactive context. (You tried to do something that can only be done from inside a reactive expression or observer.)

server <- function(input, output) {
    #fileA import
    A <- reactive(
        read.csv(
            input$fileA$datapath,
            header = input$header,
            sep = input$sep,
            quote = input$quote
        )
    )
    #FileB import
    B <- reactive(
        read.csv(
            input$fileB$datapath,
            header = input$header,
            sep = input$sep,
            quote = input$quote
        )
    )
    
    ##subtract B from A (columns 2 and 4)
    A()[,2] <- as.numeric(A()[,2])
    B()[,2] <- as.numeric(B()[,2])
    A()[,4] <- as.numeric(A()[,4])
    B()[,4] <- as.numeric(B()[,4])
    
    Finalcosts_AB2 <- A()[,2]-B()[,2]
    Finalcosts_AB4 <- A()[,4]-B()[,4]
    
    A()[,2] <- Finalcosts_AB2
    A()[,4] <- Finalcosts_AB4
    
    output$ABdiff <- renderTable({
        req(input$filaA)
        req(input$fileB)
        return(A())})

}

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

    ui <- fluidPage(

    titlePanel("testfile"),
    
    sidebarPanel(
        #Input: select file A----
        fileInput(
            "fileA",
            "Upload fileA results (.CSV format)",
            multiple = FALSE,
            accept = c("text/csv", "text/comma-separated-values,
                                    text/plain", ".csv")
        ),
        #Horizontal line
        tags$hr(),
        #Input: select file B----
        fileInput(
            "fileB",
            "Upload fileB results (.CSV format)",
            multiple = FALSE,
            accept = c("text/csv", "text/comma-separated-values,
                                    text/plain", ".csv")
        ),
        #Horizontal line
        tags$hr(),
        #settings
        # 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"
        )
    ),
    mainPanel(
        #header
        h3("Results"),
        #Output: HTML table of results----
        tableOutput("ABdiff")
    )
    
    )

我原以为在导入文件A和B时使用被动语句意味着函数的其余部分在被动表达式中完成。。。也许我找错了方向。谢谢你的建议

服务器功能如下：

Error in .getReactiveEnvironment()$currentContext() : 
  Operation not allowed without an active reactive context. (You tried to do something that can only be done from inside a reactive expression or observer.)

server <- function(input, output) {
    #fileA import
    A <- reactive(
        read.csv(
            input$fileA$datapath,
            header = input$header,
            sep = input$sep,
            quote = input$quote
        )
    )
    #FileB import
    B <- reactive(
        read.csv(
            input$fileB$datapath,
            header = input$header,
            sep = input$sep,
            quote = input$quote
        )
    )
    
    ##subtract B from A (columns 2 and 4)
    A()[,2] <- as.numeric(A()[,2])
    B()[,2] <- as.numeric(B()[,2])
    A()[,4] <- as.numeric(A()[,4])
    B()[,4] <- as.numeric(B()[,4])
    
    Finalcosts_AB2 <- A()[,2]-B()[,2]
    Finalcosts_AB4 <- A()[,4]-B()[,4]
    
    A()[,2] <- Finalcosts_AB2
    A()[,4] <- Finalcosts_AB4
    
    output$ABdiff <- renderTable({
        req(input$filaA)
        req(input$fileB)
        return(A())})

}

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

    ui <- fluidPage(

    titlePanel("testfile"),
    
    sidebarPanel(
        #Input: select file A----
        fileInput(
            "fileA",
            "Upload fileA results (.CSV format)",
            multiple = FALSE,
            accept = c("text/csv", "text/comma-separated-values,
                                    text/plain", ".csv")
        ),
        #Horizontal line
        tags$hr(),
        #Input: select file B----
        fileInput(
            "fileB",
            "Upload fileB results (.CSV format)",
            multiple = FALSE,
            accept = c("text/csv", "text/comma-separated-values,
                                    text/plain", ".csv")
        ),
        #Horizontal line
        tags$hr(),
        #settings
        # 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"
        )
    ),
    mainPanel(
        #header
        h3("Results"),
        #Output: HTML table of results----
        tableOutput("ABdiff")
    )
    
    )

---

server请尽量避免修改被动数据帧。如下图所示修改服务器代码后，它就可以正常工作了

server <- function(input, output) {
  #fileA import
  A <- reactive({
    da <- read.csv(
      req(input$fileA$datapath),
      header = input$header,
      sep = input$sep,
      quote = input$quote
    )
    da[,2] <- as.numeric(da[,2])
    da[,4] <- as.numeric(da[,4])
    da
  })
  
  #FileB import
  B <- reactive({
    db <- read.csv(
      req(input$fileB$datapath),
      header = input$header,
      sep = input$sep,
      quote = input$quote
    )
    db[,2] <- as.numeric(db[,2])
    db[,4] <- as.numeric(db[,4])
    db
  })
  
  output$ABdiff <- renderTable({
    req(A(),B())
    Finalcosts_AB2 <- A()[,2]-B()[,2]
    Finalcosts_AB4 <- A()[,4]-B()[,4]
    AA <- A()
    AA[,2] <- Finalcosts_AB2
    AA[,4] <- Finalcosts_AB4
    return(AA)
  })
  
}

服务器谢谢-既然您已经指出了这一点，那么这就非常有意义了！非常感谢。