Tuesday, 24 July 2018
r - How to convert a Shiny app consisting of multiple files into an easily shareable and reproducible Shiny example?
Answer
Answer
There are resources on how to create a Minimal, Complete, and Verifiable example in general on , and on how to make a great R reproducible example. However, there are no similar guidelines for shiny questions, while adhering to certain standards makes it much more likely that quality answers will be given, and thus that your question will be resolved.
However, asking a good Shiny question can be difficult. shiny apps are often large and complex, use multiple data sources, and the code is often split over multiple files, making it difficult to share easily reproducible code with others. Even though a problem may be caused in server.R, the example is not reproducible without the contents of ui.R (and possibly other files like stylesheets or global.R). Copy-pasting the contents of all these files individually is cumbersome, and requires other users to recreate the same file structure to be able to reproduce the problem.
So; how to convert your shiny app into a good reproducible example?
Answer
Example data
Of course, all guidelines regarding sample data mentioned in the answer on the question “how to make a great R reproducible example” also hold when creating questions related to Shiny. To summarize: Make sure no additional files are needed to run your code. Use sample datasets like mtcars, or create some sample data with data.frame(). If your data is very complex and that complexity is really required to illustrate the issue, you could also use dput(). Avoid using functions like read.csv(), unless of course you have questions related to functions like fileInput.
Example code
Always reduce your code to the bare minimum to reproduce your error or unexpected behavior. This includes removing calls to additional .CSS files and .js files and removing unnecessary functions in the ui and the server.
Shiny apps often consist of two or three files (ui.R, server.R and possibly global.R), for example this demo application. However, it is preferable to post your code as a single script, so it can easily be run by others without having to manually create those files. This can easily be done by:
- wrapping your ui with
ui <- fluidPage(…), - the server with
server <- function(input,output, session) {…}, - and subsequently calling
shinyApp(ui, server).
So a simple skeleton to start with could look as follows:
library(shiny)
ui <- fluidPage(
)
server <- function(input,output,session) {
}
shinyApp(ui, server)
Working Example
So, taking all the above into account, a good Minimal, Complete, and Verifiable example for a Shiny application could look as follows:
library(shiny)
df <- data.frame(id = letters[1:10], value = seq(1,10))
ui <- fluidPage(
sliderInput('nrow', 'Number of rows', min = 1, max = 10, value = 5),
dataTableOutput('my_table')
)
server <- function(input, output, session) {
output$my_table <- renderDataTable({
df[1:input$nrow,]
})
}
shinyApp(ui, server)
Adding CSS
There are multiple ways to add custom CSS to a Shiny application, as explained here. The preferred way to add CSS to a Shiny application in a reproducible example is to add the CSS in the code, rather than in a separate file. This can be done by adding a line in the ui of an application, for example as follows:
tags$head(tags$style(HTML('body {background-color: lightblue;}'))),
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