Hi, everyone! I just ran across the reactiveValuesToList function and was curious - why and when would we want to use this? Isn't a reactiveValues object already a list?
reactiveValues object is not a list. It looks like a list from the point of view of accessing it, but its structure is more complex. And it is reactive, we cannot access its values outside of a reactive domain (defined by Shiny).
Imagine a dashboard where there are very many settings for an output. The output does not update each time when you modify one of these settings but only when you press a button (e.g., it is an expensive computation, a PDF report, etc.). When you call the expensive computation function, you can pass the arguments with
result <- expensive_calculation(a = input$a, b = input$b, ......)
After 7-8 of arguments this is no longer fun. A quicker solution is
result <- do.call(expensive_calculation, reactiveValuesToList(input))
Plus you do not need to update the code each time you add a new setting on the dashboard.
Ah, okay, got it. I went ahead and tried your example on something simple.
rv <- reactiveValues(a = 1, b = 2) isolate(do.call("paste", rv))
This gave me the error
Error in as.vector(x, "character") : cannot coerce type 'environment' to vector of type 'character'
All worked well though if I did the following (as you suggest):
 "1 2"
P.S. I was using
isolate as I was playing in the Console outside of a reactive context.
My original thinking was "if it looks like a duck and acts like a duck, then it's a duck!", where duck = list of course. It appears that a reactiveValues object is indeed not really a duck, er, list.