Density singletons

[grantmcdermott]

Fixes #300

As note in the issue thread, a simple fix for this was just filtering out the singletons preemptively:

datapoints = Filter(function(k) nrow(k) > 1, datapoints)

... But I worry that the silent dropping might be misleading. So I ended up rolling a more sophisticated version in order to allow the possibility of emitting a nice user warning, which is controllable through the new type-level singletons argument. By default, the warning is on:

pkgload::load_all("~/Documents/Projects/tinyplot/")
#> ℹ Loading tinyplot
tinytheme("clean", facet.prefix = TRUE, facet.axes = "outer")
tinyplot(~ mpg, facet = vs ~ gear, data = mtcars, type = "density")
#> Warning: Dropped 1 singleton group(s). Densities require at least 2 observations.

Example with another density type (here: violin plots):

tinyplot(mpg ~ cyl, facet = ~ gear, data = mtcars, type = "violin")
#> Warning: Dropped 2 singleton group(s). Densities require at least 2 observations.

It's also possible to silence the warning with singletons = "drop"). Our first example again:

tinyplot(~ mpg, facet = cyl ~ gear, data = mtcars,
        type = type_density(singletons = "drop"))

tinytheme()

^{Created on 2026-08-21 with reprex v2.1.1}