shiny (version 0.9.1)

reactive: Create a reactive expression

Description

Wraps a normal expression to create a reactive expression. Conceptually, a reactive expression is a expression whose result will change over time.

Usage

reactive(x, env = parent.frame(), quoted = FALSE, label = NULL)
is.reactive(x)

Value

a function, wrapped in a S3 class "reactive"

Details

Reactive expressions are expressions that can read reactive values and call other reactive expressions. Whenever a reactive value changes, any reactive expressions that depended on it are marked as "invalidated" and will automatically re-execute if necessary. If a reactive expression is marked as invalidated, any other reactive expressions that recently called it are also marked as invalidated. In this way, invalidations ripple through the expressions that depend on each other.

See the http://rstudio.github.com/shiny/tutorial/{Shiny tutorial} for more information about reactive expressions.

Examples

values <- reactiveValues(A=1)

reactiveB <- reactive({
  values$A + 1
})

# Can use quoted expressions
reactiveC <- reactive(quote({ values$A + 2 }), quoted = TRUE)

# To store expressions for later conversion to reactive, use quote()
expr_q <- quote({ values$A + 3 })
reactiveD <- reactive(expr_q, quoted = TRUE)

# View the values from the R console with isolate()
isolate(reactiveB())
isolate(reactiveC())
isolate(reactiveD())