app.R

# https://unboxed-analytics.shinyapps.io/the-potential-for-growth/
# http://unboxed-analytics.com/life-hacking/fundamentals-of-investing/

library(FinCal)
library(ggplot2)
library(tidyr)
library(shinythemes)
library(scales)

# Define UI for application that draws a histogram
ui <- shinyUI(fluidPage(theme = shinytheme("spacelab"),
  # Application title
  titlePanel("The Potential for Growth: Two Case Studies"),
  p('An interactive tool to accompany the ', a(href = 'http://unboxed-analytics.com/life-hacking/fundamentals-of-investing/', '"Fundamentals of Investing"'), 'post.'),
  
  # Sidebar with a slider input for number of bins
  sidebarLayout(
    sidebarPanel(
      numericInput(
        inputId = "rate",
        label = "Yearly Rate of Return",
        value = .06,
        min = .01,
        max = .15,
        step = .01
      ),
      p("Represented as a decimal."),
      p(".06 = 6%"),
      numericInput(
        inputId = "years",
        label = "Number of Years",
        value = 43,
        min = 3,
        max = 50,
        step = 1
      ),
      numericInput(
        inputId = "pv",
        label = "Initial Outlay",
        value = 2000,
        min = 1000,
        max = 100000,
        step = 1000.
      ),
      numericInput(
        inputId = "pmt",
        label = "Monthly Contribution",
        value = 0,
        min = 0,
        max = 10000,
        step = 100
      ),
      numericInput(
        inputId = "type",
        label = "Payment Type",
        value = 0,
        min = 0,
        max = 1,
        step = 1
      ),
      p("Indicates if payments occur at the end of each period (Payment Type = 0) or if payments occur at the beginning of each period (Payment Type = 1).")
      ),
    
    mainPanel(plotOutput("finPlot"),
              p("The grey line represents PRINCIPAL and the blue line represents PRINCIPAL + INTEREST."),
              p("Case 1: Suppose you have $2,000 to invest. You use that money to purchase a low-cost, tax-efficient, diversified mutual fund offering an approximate yearly return of 6%."),
              p("You purchase the mutual fund on your 22nd birthday and don’t check your account until your 65th birthday on the day of retirement. After 43 years, you would have over $26,200! Your money has doubled four times."),
              p("Case 2: Suppose again you have $2,000 today to invest. You purchase shares of the same mutual and now, in addition to the initial investment, purchase $100 of additional shares each month. [Adjust the 'Monthly Contribution' sidebar parameter]"),
              p("How much would you have at the end of 43 years? Over $268,400! You have passively created wealth through the market."))
  )
))

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

    # processing
    total <- fv(r = input$rate/12, n = 0:(12*input$years), pv = -input$pv, pmt = -input$pmt, type = input$type)
    principal <- seq(input$pv, input$pv + (input$years*12)*(input$pmt+.000000001), input$pmt + .000000001)
    interest <- total - principal
    df <- data.frame(period = 0:(12*input$years), total, principal)
    
    # plotting
    ggplot(df, aes(x = period)) + 
      geom_line(aes(y = total), col = "blue", size = .85) +
      geom_line(aes(y = principal), col = "black", size = .85) +
      labs(x = "Period",
           y = "") + 
      scale_y_continuous(labels = dollar) +
      theme(legend.position="bottom") +
      theme(legend.title = element_blank()) +
      theme_minimal()
  })
})

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