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dynamic_modules.html
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<!DOCTYPE html>
<html lang="" xml:lang="">
<head>
<title>Dynamically adding and removing Shiny modules</title>
<meta charset="utf-8" />
<meta name="author" content="Jonas Hagenberg" />
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<link rel="stylesheet" href="xaringan-themer.css" type="text/css" />
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<body>
<textarea id="source">
class: center, middle, inverse, title-slide
# Dynamically adding and removing Shiny modules
### Jonas Hagenberg
### Appsilon Shiny Conference
### 27.04.2022
---
# Code availability
Find the code on github:
https://github.com/jonas-hag/dynamic_shiny_modules
---
# Dynamic modules
- modules are either called when initialising the Shiny app or dynamically
--
- dynamic modules can be useful when:
- something has to be repeated based on user input
- e.g. show several plots or tables
- a set of UI elements
--
- can become complex easily -> use it with care!
???
- set of UI elements: e.g. additional layers in plots that can be controlled
- how to get from static modules to dynamically added modules? -> livecoding
---
# Selectors
- used in `jQuery`, the JavaScript framework used by Shiny
- based on CSS selectors
- can select e.g. element types
- for us relevant: select elements by `id`
---
# Adding modules
When adding a module:
- call the module `server` function
- insert the module UI elements with `insertUI`
- use an appropriate `selector` where to insert the UI - one can use an empty `div`
with an `id`
- use a different `id` for every added module instance
---
# How to remove a module
- remove UI part with `removeUI`
- needs to provide a selector
- works well for one UI element but not for several in module UI
- wrap UI elements with `div` with module `id` instead of `tagList`
```r
module_UI <- function(id) {
ns <- NS(id)
* div(
id = id,
# your UI elements here
)
}
```
???
- the selector is based on the id of the UI elements
- in our case the id of the module
---
# Recap: remove UI of a module
- use `removeUI`
- create a selector with `#` and the module `id`
- use a unique `id` for every module
???
- this removes the contents of the module on the client side
---
# How to remove the server part
- so far, only UI elements were removed
- `input`s, `reactive`s and `observeEvent`s of the module are still in
the server part
- can negatively influence the performance
- therefore also remove these
---
# Remove `input`s
- `input`s are still stored on the serve side and consume memory
--
```r
remove_shiny_inputs <- function(id, .input) {
invisible(
lapply(grep(id, names(.input), value = TRUE), function(i) {
* .subset2(.input, "impl")$.values$remove(i)
})
)
}
```
By [Thomas Roh](https://roh.engineering/posts/2020/02/shiny-add/removing-modules-dynamically/), CC BY-NC 4.0
???
- pass the `id` of the module that should be removed (`id`), the different inputs
are matched automatically
- pass the list (here: `input`) where the inputs are stored
- for every module input, call the `remove` method
- rather hacky method, not Shiny official
- currently don't know a way to remove `reactive` expressions
---
# Destroy `observeEvent`s
- you can also destroy `observeEvent`s from removed modules
- please check out the additional information section of the repository
- check out the [Appsilon Blog Post](https://appsilon.com/how-to-safely-remove-a-dynamic-shiny-module/)
---
# Summary
- use `insertUI`/`removeUI` for the module UI
- remove inputs and destroy `observeEvent`s to clean up the server side and
avoid performance issues
- use unique `id`s to avoid problems
- use dynamic addition/removal only sparingly
</textarea>
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