Thread by @WeAreRLadies

💡 What is reactivity and what does it have to do with a carrier pigeon? 🐦

To better understand how a #ShinyApp works, it's good to understand what's behind reactivity.

To describe it, I love the image of a carrier pigeon 🐦 (I picked up this idea when reading a post by @StatGarrett - so all credits go to him and all errors are mine ✨)

@StatGarrett What reactivity does is "a magic trick [that] creates the illusion that one thing is happening, when in fact something else is going on" (shiny.rstudio.com/articles/under…).

@StatGarrett Your ShinyApp only re-runs those parts where it is necessary. But what does this have to do with a carrier pigeon? Have a look at the GIF:

@StatGarrett It shows your ShinyApp with the UI 👤 (bottom right) and the server 🧠 (top right). The user (bottom left) asks for something 🙋🏼‍♀️

@StatGarrett In the first round, the user asks for "Rwanda" and - after checking, the ShinyApp does not re-run because it already shows Rwanda. ✅

@StatGarrett In the next round, the user asks for "Rwanda" and "Angola" - the ShinyApp evaluates and initiates a re-run to update the requested selection. Here comes the carrier pigeon 🐦 It starts sending the signal to update to the server.

@StatGarrett Once it has delivered the message, it comes back to where it started and waits until it gets a new message to deliver (just like a carrier pigeon 😊). So, there is only some kind of action (such as updating the plot) if necessary.

@StatGarrett This was a simple wrap-up of Garrett's post - if you want to know more about reactive values and observers, have a look here: shiny.rstudio.com/articles/under… 👩🏼‍💻