Async programming in Shiny plus Spinners
Greetings earthlings!
If you are reading this, you already know the power and beauty of Shiny, so I won’t spend your time explaining this.
Last week I had a task job to async a part of the code because it was freezing the entire application. For those that don’t know, the Shiny works in a sync way, which means it executes code in sequence, so if you click on one button and it has a long operation, the entire application will wait until the operation ends.
To exemplify, I create a simple app with two extensive operations. The data you will find here consists of the distance between pairs of each city in the State of Parana in Brazil, some geographics coordinations and sf things to create maps. And we will be using the idea of Travel Salesman to illustrate. We will calculate all the possible routes between the cities you select, considering that the first one is the origin and seeing which ones have the shortest route.
So, what is the idea? You can select a pool of cities, between a minimum of three and a max of seven, that is because less than three, no makes sense, and great than seven will take too much time.
After you choose your cities, a distance matrix between pair of cities will appear and two spinners. The left of the distance matrix is all the possible routes in a DT, the first one is the shortest route, and the second spinner below the distance matrix is a moving plot. The scenario with seven cities will generate 720 plots, 6!, because, remember, the first city is our origin.
So, we have two async operations, the first one that generates all possible routes to be taken, and the second one that depends on the previous one to generate all the plots.
You’ll see that each element appears in Shiny dependable, so no more freezing problems.
The code can be find here
Thank you for reading and hasta la vista muchachos.
To know more about async things in Shiny
