R Academy · Lesson

Dynamic UI with renderUI and insertUI

Generate UI elements on-the-fly based on user input and server state.

Dynamic UI — Why and When

Sometimes the UI you need cannot be fully determined at app startup — it depends on user choices, loaded data, or runtime conditions. Shiny provides two mechanisms: renderUI() for replacing a placeholder's entire contents, and insertUI()/removeUI() for adding or removing elements without replacing everything.

library(shiny)

# Static UI: columns always shown
# ui <- fluidPage(selectInput('x', ...), selectInput('y', ...))

# Dynamic UI: columns depend on which dataset was loaded
# ui <- fluidPage(fileInput('upload', ...), uiOutput('var_selectors'))

renderUI() and uiOutput()

renderUI({...}) in the server builds and returns a UI element reactively. uiOutput('id') in the UI creates a placeholder that displays whatever renderUI produces. The entire content of the placeholder is replaced each time the reactive reruns.

ui <- fluidPage(
  selectInput('dataset', 'Dataset:', choices = c('iris', 'mtcars')),
  uiOutput('column_selector')   # placeholder
)

server <- function(input, output, session) {
  output$column_selector <- renderUI({
    df <- get(input$dataset)  # reactive dependency on dataset
    selectInput('col', 'Choose Column:',
                choices = names(df))
  })
}

shinyApp(ui, server)

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