Proper functioning of any teal
application requires the presence of a teal_data
object.
Typically, a teal_data
object created in the global environment will be passed to the data
argument in init
.
This teal_data
object should contain all elements necessary for successful execution of the application's modules.
In some scenarios, however, application developers may opt to postpone some data operations until the application runtime.
This can be done by passing a special shiny
module to the data
argument.
The teal_data_module
function is used to build such a module from the following components:
id
; defines user interface elements for the data moduleid
; defines server logic for the data module, including data creation; must return a reactive expression containing a teal_data
objectteal
will run this module when the application starts and the resulting teal_data
object that will be used throughout all teal
(analytic) modules.
One case for postponing data operations is datasets that are dynamic, frequently updated.
Such data cannot be created once and kept in the global environment.
Using teal_data_module
enables creating a dataset from scratch every time the user starts the application.
library(teal)
data_module <- teal_data_module( ui = function(id) div(), server = function(id) { moduleServer(id, function(input, output, session) { reactive({ data <- within( teal_data(), { dataset1 <- iris dataset2 <- mtcars } ) datanames(data) <- c("dataset1", "dataset2") # optional data }) }) } ) app <- init( data = data_module, modules = example_module() ) if (interactive()) { shinyApp(app$ui, app$server) }
See ?qenv
for a detailed explanation of how to use the within
method.
Another reason to postpone data operations is to involve the application user in the preprocessing stage. An initial, constant form of the data can be created in the global environment and then modified once the app starts.
The following example illustrates how teal_data_module
can be utilized to subset data based on the user inputs:
data <- within(teal_data(), { dataset1 <- iris dataset2 <- mtcars }) datanames(data) <- c("dataset1", "dataset2") data_module <- teal_data_module( ui = function(id) { ns <- NS(id) div( selectInput(ns("species"), "Select species to keep", choices = unique(iris$Species), multiple = TRUE ), actionButton(ns("submit"), "Submit") ) }, server = function(id) { moduleServer(id, function(input, output, session) { eventReactive(input$submit, { data_modified <- within( data, dataset1 <- subset(dataset1, Species %in% selected), selected = input$species ) data_modified }) }) } ) app <- init( data = data_module, modules = example_module() ) if (interactive()) { shinyApp(app$ui, app$server) }
Note that running preprocessing code in a module as opposed to the global environment will increase app loading times. It is recommended to keep the constant code in the global environment and to move only the dynamic parts to a data module.
When using teal_data_module
to modify a pre-existing teal_data
object, it is crucial that the server function and the data object are defined in the same environment, otherwise the server function will not be able to access the data object.
This means server functions defined in packages cannot be used.
teal_data_modules
The server logic of a teal_data_module
can be modified before it is used in an app, using the within
function.
This allows the teal_data
object that is created in the teal_data_module
to be processed further.
In the previous example, data_module
takes a predefined teal_data
object and allows the app user to select a subset.
The following example modifies data_module
so that new columns are added once the data is retrieved.
data_module_2 <- within( data_module, { # Create new column with Ratio of Sepal.Width and Petal.Width dataset1$Ratio.Sepal.Petal.Width <- round(dataset1$Sepal.Width / dataset1$Petal.Width, digits = 2L) # Create new column that converts Miles per Galon to Liter per 100 Km dataset2$lp100km <- round(dataset2$mpg * 0.42514371, digits = 2L) } ) app <- init( data = data_module_2, modules = example_module() ) if (interactive()) { shinyApp(app$ui, app$server) }
Any scripts or data that you put into this service are public.
Add the following code to your website.
For more information on customizing the embed code, read Embedding Snippets.