inst/shiny-examples/Triplot/app.R

In bayesball/ShinyBayes: Shiny Apps for Bayesian Inference

library(shiny)
library(ggplot2)
library(gridExtra)

# Define UI ----
ui <- fluidPage(
  # Application title
  titlePanel("Bayes Triplot"),

  # Sidebar with a slider input for the number of bins
  sidebarLayout(
    sidebarPanel(
      sliderInput("a",
                  "Beta Shape Parameter a:",
                  min = 1,
                  max = 30,
                  value = 4,
                  step = 0.2),
      sliderInput("b",
                  "Beta Shape Parameter b:",
                  min = 1,
                  max = 30,
                  value = 4,
                  step = 0.2),
      sliderInput("s",
                  "Number of Successes:",
                  min = 0,
                  max = 50,
                  value = 0),
      sliderInput("f",
                  "Number of Failures:",
                  min = 0,
                  max = 50,
                  value = 0)
    ),

    # Show a plot of the generated distribution
    mainPanel(
      tabsetPanel(type = "tabs",
                  tabPanel("Description",
                           br(),
                           h4('Description'),
                           p("This app shows a Bayesian
                             triplot for the situation where one
                             has binomial data and a beta prior is
                             assigned to the proportion."),
                           h4('Using the App'),
                           p('One uses the sliders to choose the
                             shape parameters a and b for the beta
                             prior and the number of successes and
                             failures in the sample.  The triplot
                             displays the prior density, the normalized
                             likelihood and the posterior density.  One
                             sees how the posterior combines the
                             information in the prior and the data.')),
                  tabPanel("Triplot",
                        plotOutput("distPlot",
                           height="450px")))
    )
  ))

# Define server logic ----
server <- function(input, output) {
  gtriplot <- function(a, b, s, f){

    p <- seq(0, 1, length.out = 200)
    prior <- data.frame(p = p,
                        Density = dbeta(p, a, b),
                        Type = "Prior")
    like <- data.frame(p = p,
                       Density = dbeta(p, s + 1, f + 1),
                       Type = "Likelihood")
    post <- data.frame(p = p,
                       Density = dbeta(p, a + s, b + f),
                       Type = "Posterior")
    dall <- rbind(prior, like, post)

    text <- paste("Beta(", a, ", ",
                  b, ") Prior, (s, f) = (",
                  s, ", ", f,")", sep = "")

    ggplot(dall, aes(p, Density, color = Type)) +
      geom_line(size = 1.5) +
      ggtitle(paste("Triplot: ", text)) +
      theme(plot.title = element_text(colour = "red",
                                      size = 24,  hjust = 0.5,
                                      vjust = 0.8, angle = 0)) +
      theme(text = element_text(size = 18)) +
      xlab("P") + ylab("Density")
  }

    output$distPlot <- renderPlot({
      gtriplot(input$a, input$b,
               input$s, input$f)
    })
}

# Run the app ----
shinyApp(ui = ui, server = server)