Project 0: Our First App

The Main File, app.R

Go to projects -> project0-first-app and open app.R.

• This file contains all the components of the app: the user interface and reactive logic.

• The UI and reactive logic can be written in separate .R files that are sourced in app.R or all put in the same file.

• In this case the UI is in user_interface.R and the reactive logic is in reactive_logic.R.

shinyApp()

app.R is just a regular R script

• Adding the call to shinyApp() at the end of the script changes the “Run” button to “Run App”

Starting in the Muggle World

Let’s start with muggle.R (our run-of-the-mill R code)

• We load the libraries we need

• We create a function muggle_plot that takes variable names from the diamonds dataset as inputs and generates a scatterplot

• Test it out if you want by uncommenting and running the last line of the script

User Interface

Open user_interface.R

• The function tagList takes HTML functions as inputs and creates a list of HTML components

• Try running the first line, h2("A very basic Shiny app") in the console (make sure you have shiny loaded)

• Functions like h2, p, and actionButton are wrappers for HTML code (essentially strings)

• The first argument in actionButton, plotOutput, and textOutput are IDs. We will use these IDs in the next part

Reactive Logic

Open reactive_logic.R

• We will connect the UI to the Muggle code with reactive logic

• We are assigning a function to reactive_logic with three arguments: input, output, and session. The arguments are always the same, but reactive_logic is usually called server.

• Functions renderPlot and renderText are assigned to output$IDname. They correspond to the UI functions plotOutput and textOutput

Invoking the App

shinyApp(user_interface, reactive_logic)

To run our app, we use the command shinyApp. The first argument is the UI, and the second argument is our reactive logic.

Deploying the App

1. Put all the files your app needs in a single directory (the name of the directory will be the name of the app)

2. Make sure there is a file called app.R with the call to shinyApp()

3. Run rsconnect::deployApp("/path/to/app/directory"). You may need to connect your shinyapps.io account to deploy an app for the first time.

Your Turn: Modify the App

Try the following on your own!

1. Hide the button message until the button has been clicked 3 times.

2. Add selectInput dropdown menus for the X and Y variables.

3. (Superstar) Connect the selectInput menus to the plot (we haven’t covered this yet)