Track the axis limits a plot should draw with

Modules derive an axis range on the server and push it into their own y.min/y.max controls with updateNumericInput(), which is a client round-trip: the plot renders once with the stale limits and again when the browser echoes the new ones. setup_axis_range() gives the plot a server-side value to read instead, held in a shiny::reactiveVal() that only invalidates on a real change, so the echo costs nothing while a limit the user types comes straight through.

Usage

setup_axis_range(
  input,
  session,
  min_key = "y.min",
  max_key = "y.max",
  headroom = NULL,
  params = NULL
)

Arguments

input: The Shiny input object from inside moduleServer().
session: The Shiny session object from inside moduleServer().
min_key, max_key: Character strings — the limit controls' input ids, without namespacing.
headroom: Optional function of no arguments returning the smallest acceptable maximum, or NULL for none. Returning NULL or a non-finite value leaves the requested maximum alone.
params: Optional reactive-defaults store from setup_reactive_defaults(), or NULL. A limit backed by the store follows it rather than the client input.

Value

A shiny::reactiveVal() holding list(min = , max = ). Call it with no arguments to read, and with a value to seed.

Details

Pass headroom when something is drawn above the data that the limits have to clear — significance brackets, for instance, via stat_bracket_y_max(). It is evaluated reactively, and the maximum is raised to meet it whenever the requested one falls short; the control is updated to match, so the number on screen is the limit actually in use rather than one the plot has quietly overridden. The maximum is only ever raised this way, so a larger limit the user chose is left alone.

Seed the store alongside any update*Input() call that sets the limits (the y-data observer, the Reset button) so the echo arrives as a no-op:

y_range_store(list(min = y_range$min, max = y_range$max))
updateNumericInput(session, "y.min", value = y_range$min)
updateNumericInput(session, "y.max", value = y_range$max)

Author

Jared Andrews

Examples

if (interactive()) {
    library(shiny)

    server <- function(input, output, session) {
        y_range_store <- setup_axis_range(
            input, session,
            headroom = function() {
                if (!isTRUE(input$stats.enabled)) {
                    return(NULL)
                }
                stat_bracket_y_max(iris, x = "Species", y = "Sepal.Length")
            }
        )

        output$plot <- renderPlot({
            lims <- y_range_store()
            plot(iris$Sepal.Length, ylim = c(lims$min, lims$max))
        })
    }
}