Have different constructor for "Data" module and "Transform" module

[vedhav]

Adds teal_transform_module() to be used to create data modules for transformation.

Example usage

library(teal)
data <- teal_data() %>%
  within({
    iris <- iris
    mtcars <- mtcars
  })
my_transformers <- list(
  teal_transform_module(
    label = "Custom transform for iris",
    ui = function(id) {
      ns <- NS(id)
      tags$div(
        numericInput(ns("n_rows"), "Number of rows to subset", value = 6, min = 1, max = 150, step = 1)
      )
    },
    server = function(id, data) {
      moduleServer(id, function(input, output, session) {
        reactive({
          data() %>%
            within(
              {
                iris <- head(iris, num_rows)
              },
              num_rows = input$n_rows
            )
        })
      })
    }
  )
)
app <- init(
  data = data,
  modules = example_module(transformers = my_transformers)
)
if (interactive()) {
  shinyApp(app$ui, app$server)
}

[gogonzo]

Please link [teal_transform_module()] in description transformers argument in docs of teal_module function. Please review current teal_module and teal_transform_module documentation and write comprehensive description aimed for app developer - app developer needs to know everything about how teal_transform_module and teal_module works, but don't need to know FilteredData. What I mean by this is that you did right writing "passed through filter panel" but writing "modules" should not occur in this case. App developer needs to understand that teal_data object is sequenced through all teal_transform_modules' servers (it is a list) and eventually it is handed over to the server of teal_module

Roxygen docs should be more technical, while vignette should be focused on usage

Would be nice if @donyunardi looked at this content

[donyunardi]

Provided some alternative to the content.

[donyunardi]

Since we're only using one teal_transform_module, perhaps we don't need to wrap it in a list? This will set the stage for the next example when we do have multiple teal_transform_modules wrapped in a list.

[gogonzo]

I guess it makes sense, but let me think about this. Currently we have:

• module is wrapped by modules
• teal_slice is wrapped teal_slices
• teal_data_module is not wrapped by anything
• teal_transform_module is wrapped by list()

[donyunardi]

Should we use a very simple module() so that it's clear that transformer is passed as an argument to this function?

[gogonzo]

Yes, I think vignette should elaborate more about creating module which consumes transformers.

I've updated description here: #1231