Reactivity: composed reactive variable
Whenever the value of a reactive variable (or an input) changes, the code that uses this reactive variable is re-executed. To determine what code runs when a reactive variable changes its value, Shiny creates a dependency graph from the code. In general, if x
depends on y
and y
depends on z
, then modifying z
causes y
to update, which in turn triggers x
to update.
Here is an example of a reactive variable that depends on another reactive variable:
x <- reactive({
input$num1 + 5
})
y <- reactive({
x() + input$num2
})
In the code above, when does the value of y
get updated?
This exercise is part of the course
Case Studies: Building Web Applications with Shiny in R
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