Create a non-reactive scope for an expression
Executes the given expression in a scope where reactive values or expression can be read, but they cannot cause the reactive scope of the caller to be re-evaluated when they change.
isolate(expr)
expr |
An expression that can access reactive values or expressions. |
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 expression's value.) The isolate
function lets you read a reactive value or expression without establishing this
relationship.
The expression given to isolate() is evaluated in the calling
environment. This means that if you assign a variable inside the
isolate(), its value will be visible outside of the isolate().
If you want to avoid this, you can use base::local() inside the
isolate().
This function can also be useful for calling reactive expression at the
console, which can be useful for debugging. To do so, simply wrap the
calls to the reactive expression with isolate().
## Not run:
observe({
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)
})
observe({
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)
})
observe({
x <- 1
# x outside of isolate() is affected
isolate(x <- 2)
print(x) # 2
y <- 1
# Use local() to avoid affecting calling environment
isolate(local(y <- 2))
print(y) # 1
})
## End(Not run)
# Can also use isolate to call reactive expressions from the R console
values <- reactiveValues(A=1)
fun <- reactive({ as.character(values$A) })
isolate(fun())
# "1"
# isolate also works if the reactive expression accesses values from the
# input object, like input$xPlease choose more modern alternatives, such as Google Chrome or Mozilla Firefox.