for loop in reactive function: incompatible types (from closure to logical) in subassignment type fix

Question

I am starting with shiny apps and would like to create a credit-calculator in a shiny app. However, it looks like I have a problem to implement a for-loop to create the output data.

UI

library(shiny)
shinyUI(
  fluidPage(
    titlePanel("User information"), # TITLE CONTENT
    sidebarLayout(
      sidebarPanel(("Enter your Information here"),
                   numericInput("credit.amount",
                             "How much is your credit?",
                             "")
                   ,sliderInput("yr.inter", 
                             "Interrest rate p.a.",
                             min = 0.5, 
                             max = 20, 
                             value = 8.5, 
                             step = 0.5
                             )
                   ,numericInput("mthl.rate",
                              "Your monthly payment",
                              "")
                   ), # SIDE BAR CONTENT
      mainPanel(("Credit decay"),
                textOutput("decaytime")
                ,tableOutput("creditmod")
                # ,textOutput("")
                ) # MAIN PANEL CONTENT
    )
  )
)

SERVER

library(shiny)
library(dplyr)
shinyServer(
  function(input, output){

    mthl.inter = reactive((input$yr.inter/1200)) # NUMERIC INPUT
    credit.amount = reactive(input$credit.amount) # SLIDER INPUT
    mthl.rate = reactive(input$mthl.rate) # NUMERIC INPUT

    # calculate repayment time

    credit.decay = reactive(
      as.numeric((log(1 - (mthl.inter() * credit.amount() / mthl.rate())) / 
        log(1 + mthl.inter())) * -1)
      ) 

    # calculate credit model 

    credit.model <- reactive({
      credit.df <- data.frame(rep(NA, credit.decay() %>% ceiling()))
      credit.df[1,1] <- credit.amount

      for (n in 2:(credit.decay() %>% ceiling()) ){
        credit.df[n,1] = credit.df[n-1,1] * (1 + mthl.inter()) - mthl.rate()
      }

      return(credit.df)

    })


    output$decaytime = renderText(credit.decay() %>% ceiling())
    output$creditmod = renderTable(credit.model())
  }
)

This returns the following error:

Warning: Error in <-: incompatible types (from closure to logical) in subassignment type fix

Your answers are very appreciated. Thank you very much, Max

Answer 1

Welcome to stackoverflow!

You'll need req() to make sure no empty user inputs are passed to your function. Furthermore, I debounced your inputs to delay the calculation a little (so the user has some time to finish his inputs before the calculation starts)

However it seems that you calculation only works for certain ratios of credit.amount and mthl.rate. You might need to add some further checks here.

Please check the following:

library(shiny)
library(dplyr)

ui <- fluidPage(
  titlePanel("Farm Statistic"), # TITLE CONTENT
  sidebarLayout(
    sidebarPanel(("Enter your Farm Information here"),
                 numericInput("credit_amount",
                              "How much is your credit?",
                              NA),
                 sliderInput("yr_inter", 
                              "Interrest rate p.a.",
                              min = 0.5, 
                              max = 20, 
                              value = 8.5, 
                              step = 0.5
                 ),
                 numericInput("mthl_rate",
                               "Your monthly payment",
                               NA)
    ), # SIDE BAR CONTENT
    mainPanel(("Credit decay"),
              textOutput("decaytime"),
              tableOutput("creditmod")
              # , textOutput("")
    ) # MAIN PANEL CONTENT
  )
)

server <- function(input, output, session) {

  mthl.inter.tmp <- reactive({req(input$yr_inter/1200)}) # NUMERIC INPUT
  credit.amount.tmp <- reactive({req(input$credit_amount)}) # SLIDER INPUT
  mthl.rate.tmp <- reactive({req(input$mthl_rate)}) # NUMERIC INPUT

  mthl.inter <- debounce(mthl.inter.tmp, 500)
  credit.amount <- debounce(credit.amount.tmp, 500)
  mthl.rate <- debounce(mthl.rate.tmp, 500)

  # calculate repayment time
  credit.decay = reactive({
    req(mthl.inter(), credit.amount(), mthl.rate())
    as.numeric((log(1 - (mthl.inter() * credit.amount() / mthl.rate())) / log(1 + mthl.inter())) * -1)
    }) 

  # calculate credit model 
  credit.model <- reactive({
    req(credit.decay())
    credit.df <- data.frame(rep(NA, credit.decay() %>% ceiling()))
    credit.df[1,1] <- credit.amount()

    for (n in 2:(credit.decay() %>% ceiling()) ){
      credit.df[n,1] = credit.df[n-1,1] * (1 + mthl.inter()) - mthl.rate()
    }

    return(credit.df)

  })

  output$decaytime = renderText(credit.decay() %>% ceiling())
  output$creditmod = renderTable(credit.model())
}

shinyApp(ui, server)