24-shiny2

Author
Affiliation

Prof Amanda Luby

Carleton College
Stat 220 - Spring 2025

Understanding Reactivity

Your group’s task is to improve a Shiny app through the use of reactive expressions. To do this, you will identify flaws in the above version of the Shiny app and edit the code to implement solutions.

This activity will guide your through the adaptation of this Shiny app.

Part 1: on your own

Start by downloading 24-reactivity.R

  1. To begin, you need to understand what the Shiny app is doing. Run the Shiny app. What output changes when you change…

  1. the number of bootstrap resamples?

  2. the number of histogram bins?

  3. the confidence level?

  1. Looking back at #1, are there any surprises? Does anything change/update unexpectedly? Does anything fail to update?

Part 2: with those around you (I recommend groups of 3)

  1. Discuss your answers to Part 1 with your group and be ready to report back.

  2. Read through the code in the renderPlot() and renderPrint() reactive expressions. Note the key tasks executed within each.

  3. Based on your answers to #4, Is there any replication? That is, are any key tasks executed multiple times? Record your group’s answers and be ready to report back.

Stop here

Stop here and let Amanda know that you’ve finished. We’ll regroup and discuss reactivity shortly

Part 3

  1. Create a list of reactive values/expressions that should be created outside the render* statements. Recall that reactive values are the inputs/objects that observers watch for updates.

  2. For each reactive expression you identify in step #6, identify which output (the histogram or the confidence interval) should observe that expression and update when it is changed?

  3. Use your answers to steps #6-7 to reorganize the server-side code for this Shiny app. (You don’t need to change the inputs!) To do this, first create any reactive expressions. Next, adapt the renderPlot() and renderPrint() chunks to use your reactive expressions. Remember to run your app regularly to help pinpoint bugs.

  4. Compare and contrast the performance and readability of the revised app’s code to the original “non-modularized” version.

Stop here

Stop here and let Amanda know that you’ve finished.

manager-survey app

Finish 23-app1.R from last time. Ask if you have questions!