11.15 LOADING THINGS (2)

Code outside server <- function(input, output) {} is run once, when you launch your app
Code inside server <- function(input, output) {} is run once each time a user visits your app
Code inside render* functions is rerun constantly (not only when user changes widget value, see [reactivity(http://shiny.rstudio.com/articles/understanding-reactivity.html)])
That means…
- Load Source scripts, libraries, and data outside of server function (at the beginning)
  - Store data in www/ folder in your app directory
  - Access with read.table("www/swiss.csv", sep=",")
  - Access online data by inserting the url into the read* function (e.g. read.table())
- User specific objects (e.g. object that records user’s session information) are defined inside shinyServer’s unnamed function, but outside of any render* calls
  - e.g. user registers himself, user data as input data (compare income)
- Code/objects that are affected by choices in widgets must be placed witin the a render* function
  - Shiny reruns code in a render* chunk each time a user changes a widget mentioned in the chunk
Avoid placing code within render function that does not need to be there… for performance reasons!
Example

data <- read.table("http://paulcbauer.eu/wp-content/uploads/2016/10/swiss.csv", sep=",")
# data <- read.table("data/swiss.csv", sep=",")

ui <- fluidPage(
  
  titlePanel("Displaying reactive output"),
  sidebarLayout(
    sidebarPanel(
      selectInput("selection", label = h3("Select box"),
                  choices = list("Fertility" = "Fertility",
                                 "Agriculture" = "Agriculture",
                                 "Examination" = "Examination",
                                 "Education" = "Education",
                                 "Catholic" = "Catholic",
                                 "Infant.Mortality" = "Infant.Mortality"), selected = 1)
    ),

    mainPanel(
      plotOutput("distPlot"),
      textOutput("text1")
    )))


server <- function(input, output) {
  
  output$distPlot <- renderPlot({
    x    <-   data[, input$selection]
    hist(x, col = 'darkgray', border = 'white', xlab=input$selection, main="Swiss French Provinces Fertility and Socioeconomic Indicators (1888) Data")
  })
  output$text1 <- renderText({
    input$selection
  })
}
shinyApp(ui = ui, server = server)