shiny (version 0.3.0)

isolate: Create a non-reactive scope for an expression

Description

Executes the given expression in a scope where reactive values or functions can be read, but they cannot cause the reactive scope of the caller to be re-evaluated when they change.

Usage

isolate(expr)

Arguments

expr

An expression that can access reactive values or functions.

Details

Ordinarily, the simple act of reading a reactive value causes a relationship to be established between the caller and the reactive value, where a change to the reactive value will cause the caller to re-execute. (The same applies for the act of getting a reactive function's value.) The isolate function lets you read a reactive value or function without establishing this relationship.

Examples

observer(function() {
  input$saveButton  # Do take a dependency on input$saveButton

  # isolate a simple expression
  data <- get(isolate(input$dataset))  # No dependency on input$dataset
  writeToDatabase(data)
})

observer(function() {
  input$saveButton  # Do take a dependency on input$saveButton

  # isolate a whole block
  data <- isolate({
    a <- input$valueA   # No dependency on input$valueA or input$valueB
    b <- input$valueB
    c(a=a, b=b)
  })
  writeToDatabase(data)
})