R Shiny：反应性错误

Question

我正在构建我的第一个 Shiny 应用程序，目的是创建一个抵押贷款计算器和可调整的摊销计划。我能够获得以下代码以使用 runApp() 进行渲染，但它不起作用（即，不输出任何值，也不显示图形）。此外，它会在 RStudio 的控制台中生成以下错误：

“.getReactiveEnvironment()$currentContext() 中的错误： 如果没有活动的反应上下文，则不允许操作。 （您试图做一些只能在反应式表达式或观察者内部完成的事情。）"

对于背景，我正在运行： Win 7、64 位操作系统 | R v3.1.1 | RStudio v0.98.944

并尝试执行此处定义的程序，但没有成功： Shiny Tutorial Error in R R Shiny - Numeric Input without Selectors

ui.R

library(shiny)
shinyUI(
      pageWithSidebar(
      headerPanel(
            h1('Amoritization Simulator for Home Mortgages'), 
            windowTitle = "Amoritization Simulator"
      ),
      sidebarPanel(
            h3('Mortgage Information'),
            h4('Purchase Price'),
            p('Enter the total sale price of the home'),
            textInput('price', "Sale Price ($USD)", value = ""),
            h4('Percent Down Payment'),
            p('Use the slider to select the percent of the purchase price you 
              intend to pay as a down payment at the time of purchase'),
            sliderInput('per.down', "% Down Payment", value = 20, min = 0, max = 30, step = 1),
            h4('Interest Rate (APR)'),
            p('Use the slider to select the interest rate of the loan expressed
              as an Annual Percentage Rate (APR)'),
            sliderInput('apr', "APR", value = 4, min = 0, max = 8, step = 0.125),
            h4('Term Length (Years)'),
            p('Use the buttons to define the term of the loan'),
            radioButtons('term', "Loan Term (Years)", choices = c(15, 30), selected = 30),
            submitButton('Calculate')
            ),
      mainPanel(
            h3('Payment and Amoritization Simulation'),
            p('Use this tool to determine your monthly mortgage payment, 
              how much interest you will owe over the life of the loan, and how 
              you can reduce that amount with additional payment'),
            h4('Monthly Payment (Principal and Interest)'),
            p('This is the amount (in $USD) you would pay each month for a 
              mortgage under the terms you defined'),
            verbatimTextOutput("base.monthly.payment"),
            h4('Total Interest Over Life of Loan'),
            p('If paying just that amount per month, this is the total amount 
              in $USD you will spend on interest for that loan'),
            verbatimTextOutput("base.total.interest"),
            h4('Additional Principal Simulation'),
            p('One way to reduce the interest expense is to pay more principal 
              each month. Use the slider below to select an additional amount to
              include with your payment and see the reduction in interest expense
              for the life of the loan.'),
            sliderInput('add', "Additional Principal ($USD)", value = 250, min = 0, max = 1000, step = 25),
            p('Interest costs saved with this additional principal (in $USD)'),
            verbatimTextOutput("savings"),
            p('You will also pay the loan off the loan this many months early'),
            verbatimTextOutput("early"),
            plotOutput('plot')
            )
      )
)

服务器.R

library(shiny)
library(ggplot2)
library(scales)
shinyServer(
function(input, output) {
## determine baseline payment and interest total
price <- reactive({as.numeric(input$price)})
per.down <- reactive({input$per.down / 100})
int <- reactive({input$apr / 1200})
n <- reactive({input$term * 12})
base.monthly.payment <- (int() * price() * (1 - per.down()) * ((1 + int())^n())) / (((1 + int())^n()) - 1)
output$base.monthly.payment <- renderPrint({base.monthly.payment})
base.total.interest <- (base.monthly.payment * n()) - (price() * (1 - per.down()))
output$base.total.interest <- renderPrint({base.total.interest})
## create dataframe to populate with increments of additional payment
schedule <- data.frame(matrix(data = NA, nrow = 41, ncol = 6, 
                         dimnames = list(1:41, c("add", "add.n",
                                                "prin", "add.total.interest", 
                                                "savings", "early"))))
## initialize 'for' loop to populate possible amoritization totals
c <- 1
for (i in seq(0, 1000, 25)) {
      schedule$add[c] <- i
      schedule$add.n[c] <- log(((base.monthly.payment + i) / int()) / (((base.monthly.payment + i) / int()) - (price() * (1 - per.down())))) / log(1 + int())
      schedule$prin[c] <- round(price() * (1 - per.down()), digits = 2)
      schedule$add.total.interest[c] <- round(((base.monthly.payment + i) * schedule$add.n[c]) - schedule$prin[c], digits = 2)
      schedule$savings[c] <- round(base.total.interest - schedule$add.total.interest[c], digits = 2)
      schedule$early[c] <- round(n() - schedule$add.n[c], digits = 0)
      c <- c + 1
}
add <- reactive({input$add})
output$savings <- renderPrint({schedule$savings[which(schedule$add == add())]})
output$early <- renderPrint({schedule$early[which(schedule$add == add())]})
## create data.frame suitable for plotting
graph.data <- data.frame(matrix(data = NA, nrow = 82, ncol = 3, 
                                dimnames = list(1:82, c("add", "amount", "type"))))
c <- 1
for (i in seq(0, 1000, 25)) {
      graph.data$add[c] <- i
      graph.data$add[c + 1] <- i
      graph.data$amount[c] <- schedule$prin[which(schedule$add == i)]
      graph.data$amount[c + 1] <- schedule$add.total.interest[which(schedule$add == i)]
      graph.data$type[c] <- "Principal" 
      graph.data$type[c + 1] <- "Interest"
      c <- c + 2
}
## create plot of amoritization with line for additional principal amount
output$plot <- renderPlot({
ggplot(graph.data, aes(x = add, y = amount), color = type)
+ geom_area(aes(fill = type), position = 'stack', alpha = 0.75)
+ geom_vline(xintercept = add(), color="black", linetype = "longdash", size = 1)
+ labs(x = "Additional Principal/Month", y = "Total Cost")
+ scale_fill_manual(values=c("firebrick3", "dodgerblue3"), name = "Payment Component")
+ theme(axis.title.x = element_text(face = "bold", vjust = -0.7, size = 16), 
        axis.title.y = element_text(face = "bold", vjust = 2, size = 16),
        axis.text.x = element_text(size = 14), 
        axis.text.y = element_text(size = 14), 
        panel.margin = unit(c(5, 5, 5, 5), "mm"),
        plot.margin = unit(c(5, 5, 5, 5), "mm"),
        panel.background = element_blank(),
        panel.grid.major.y = element_line(colour = "gray"),
        panel.grid.minor.y = element_line(colour = "gray86"),
        panel.grid.major.x = element_blank(),
        panel.grid.minor.x = element_blank())
+ scale_x_continuous(labels = dollar)
+ scale_y_continuous(labels = dollar)
})
})

提前感谢您的帮助！

Answer 1

你的错误是这样的：

base.monthly.payment <- (int() * price() * (1 - per.down()) * 
  ((1 + int())^n())) / (((1 + int())^n()) - 1)

base.monthly.payment 使用 int()、n()、per.down() 和 price()，它们都是反应式的。因此base.monthly.payment 也将是被动的。因此，当您创建它/分配一个值时，您需要将其包装在 reactive 中，如下所示：

base.monthly.payment <- reactive ({
  (int() * price() * (1 - per.down()) * ((1 + int())^n())) / (((1 + int())^n()) - 1)
})

并将其称为base.monthly.payment()，就像您对n()、int() 等所做的一样。

代码中的许多其他对象也是如此，例如：schedule、base.total.interest、graph.data。