Polishing plot output: labels, watermarks, and session options

In xpose.xtras: Extra Functionality for the 'xpose' Package

knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>",
  fig.align='center'
)

library(dplyr)
library(xpose)
library(xpose.xtras)

Introduction

A model diagnostic is rarely just a diagnostic once it leaves an R session. It becomes a figure in a report, and figures in reports want consistent titles, an obvious "this is a draft" stamp while a model is still in flux, and a predictable place to land on disk. Doing all of that by hand, plot-by-plot and model-by-model, gets old fast.

xpose.xtras adds a small, composable toolkit for this last mile:

• apply_default_labs() / set_default_labs() fill in (or overwrite) plot titles, subtitles, captions and tags.
• add_watermark() / set_default_watermark() stamp a plot with draft/preliminary/confidential-style text.
• ggsave_xp() saves a plot, applying the above first, with a swappable save backend.
• plot.xpose_data() / set_default_plots() generate a whole batch of diagnostic plots from one xpdb in a single call.

All four read from the same kind of layered defaults, resolved in the same order every time: a session-wide R option, then a per-model (xpdb) default, then whatever is passed directly to the function call. set_xtras_options() and get_xtras_option() round this out by giving the whole xpose.xtras.* option family one place to be set and inspected.

Once a default is actually configured, it applies itself. print.xpose_plot() and ggsave_xp() both pick up a configured default_labs/default_watermark automatically, with nothing else to call. That behavior is controlled by the xpose.xtras.auto_apply option, TRUE unless changed; it's a no-op until something is configured, so nothing changes for existing code until a default is actually set. The functions below are still the way to configure those defaults in the first place, apply them explicitly on demand, or reach an xpdb-level default (which, unlike the option, print() has no way to pick up on its own; see the note under apply_default_labs()). The last section, [Automatic application], covers the auto-apply behavior itself.

Default labels

apply_default_labs() takes a ggplot/xpose_plot object and fills in any of title/subtitle/caption/tag that aren't already set, using (in increasing precedence) the xpose.xtras.default_labs option, an xpdb-level default, and anything passed directly.

The simplest use is a session-wide option, handy for something that should apply to every plot in a script or report, like a draft caption:

options(xpose.xtras.default_labs = list(caption = "DRAFT: do not distribute"))

p <- dv_vs_ipred(xpdb_ex_pk, quiet = TRUE)
p_labelled <- apply_default_labs(p)
p_labelled

Because dv_vs_ipred() already sets its own caption, that one wasn't touched. apply_default_labs() only fills in labels that are still empty. Passing overwrite = TRUE replaces existing labels too, and the value can use the same @keyword placeholders xpose::parse_title() understands elsewhere in the package:

apply_default_labs(p, caption = "Run @run, @nobs observations", overwrite = TRUE)
options(xpose.xtras.default_labs = NULL)

A single global caption is a blunt instrument once more than one model is in play. set_default_labs() attaches label defaults to a specific xpdb instead, and those take precedence over the option. This is useful when different models in the same report need different framing:

xpdb_draft <- xpdb_x %>%
  set_default_labs(caption = "Model @run, interim, subject to change")

dv_vs_ipred(xpdb_draft, quiet = TRUE) %>%
  apply_default_labs(xpdb = xpdb_draft, overwrite = TRUE)

apply_default_labs() can't reach back into the xpdb a plot was built from on its own. xpose's plotting functions only carry a reduced summary forward onto the plot object, not the full xpdb, so the xpdb argument has to be supplied explicitly whenever the xpdb-level tier (or @keyword resolution) should be used. Whatever is passed directly to apply_default_labs() still wins over both tiers:

dv_vs_ipred(xpdb_draft, quiet = TRUE) %>%
  apply_default_labs(caption = "Final for submission", xpdb = xpdb_draft, overwrite = TRUE)

Watermarks

add_watermark() overlays large, semi-transparent, rotated text across a plot, the kind of stamp that makes it obvious at a glance that a figure isn't final yet.

p %>%
  add_watermark()

label, colour, alpha, size, angle and fontface are all adjustable:

p %>%
  add_watermark(label = "PRELIMINARY", colour = "firebrick", alpha = 0.15, angle = 20)

The watermark is added as an ordinary ggplot2 layer, so it survives faceting and pagination: one watermark per panel, automatically:

dv_vs_ipred(xpdb_ex_pk, quiet = TRUE, facets = "SEX") %>%
  add_watermark(label = "DRAFT")

Because the watermark is drawn at a fixed rotation, it can visually merge into a plot that already has a strong diagonal of its own, like the line of unity on a dv_vs_pred() plot. The default 30 degree angle sits close to that line and gets lost among the points around it:

pred_plot <- dv_vs_pred(xpdb_ex_pk, quiet = TRUE)

pred_plot %>%
  add_watermark(alpha = 0.6)

Crossing the other way keeps the watermark clearly legible instead, without competing with the plot's own diagonal. This is exactly the kind of case angle (and alpha/size/colour) exist for:

pred_plot %>%
  add_watermark(alpha = 0.6, angle = -45)

Like the label functions, watermark settings resolve from the xpose.xtras.default_watermark option, then an xpdb-level default set with set_default_watermark(), then whatever is passed directly. A whole project can default to, say, a red "CONFIDENTIAL" stamp without repeating those arguments at every call site:

options(xpose.xtras.default_watermark = list(label = "CONFIDENTIAL", colour = "firebrick"))
p %>%
  add_watermark()
options(xpose.xtras.default_watermark = NULL)

Generating a batch of plots with plot()

Building a standard set of diagnostics for a model usually means calling several plotting functions one after another, then doing it all again for the next model. plot.xpose_data() (an S3 method for the base plot() generic) runs a whole list of plot-generating calls in one go and returns them as a flat, named list.

Called with no plots argument, it runs this package's built-in default battery: dv_vs_ipred, dv_vs_pred, res_vs_idv, res_vs_pred, eta_distrib, eta_grid, eta_vs_cov_grid, and ind_plots_sample.

default_plots <- plot(xpdb_x, quiet = TRUE)
names(default_plots)
default_plots$dv_vs_ipred

A custom plots list can mix bare functions and one-sided formulas in the ~ fn(.x) idiom used elsewhere in this package (see focus_function()). The formula form lets extra arguments be baked straight into the call, which is also how the same underlying plot function can appear more than once with different options:

custom_plots <- plot(
  xpdb_x,
  plots = list(
    xpose::dv_vs_ipred,
    ~ xpose::res_vs_idv(.x, res = "CWRES"),
    ~ xpose::res_vs_idv(.x, res = "IWRES")
  ),
  quiet = TRUE
)
names(custom_plots)

If a single entry itself returns a list of plots, that list is flattened into the overall output rather than kept nested, so the result is always a flat list regardless of what any one entry produces.

A failing plot, by default, aborts the whole call immediately (showing the original error as its cause) without returning anything -- useful when a batch of plots feeds directly into a report and a silent gap would be worse than stopping early. Passing force = TRUE instead turns a failure into a warning and skips just that entry, so the rest of plots still gets a chance to run:

flaky_plots <- plot(
  xpdb_x,
  plots = list(
    xpose::dv_vs_ipred,
    ~ stop("simulated failure"),
    xpose::eta_distrib
  ),
  force = TRUE,
  quiet = FALSE
)
names(flaky_plots)

Like default_labs/default_watermark, a project-wide plots spec can be set once via the xpose.xtras.default_plots session option (see set_xtras_options()), or attached to a specific xpdb with set_default_plots(), which takes precedence over the option. Unlike those two, though, this default is resolved as a whole rather than merged entry by entry -- a plot spec's entries aren't addressable by a stable key, since the same function can legitimately appear more than once:

xpdb_custom <- set_default_plots(xpdb_x, list(~ xpose::dv_vs_ipred(.x), ~ xpose::eta_distrib(.x)))
names(plot(xpdb_custom, quiet = TRUE))

Saving with ggsave_xp()

ggsave_xp() is a drop-in, ggplot2::ggsave()-compatible way to write a plot to disk: same plot/filename/path/width/height arguments, but it applies apply_default_labs()/add_watermark() first (apply_labs/apply_watermark, more on those in [Automatic application]), and path/width/height fall back to the xpose.xtras.save_dir/save_width/save_height options when not supplied.

out_dir <- tempdir()

saved_path <- ggsave_xp(p, filename = "dv_vs_ipred.png", path = out_dir, width = 6, height = 4)
basename(saved_path)

That's a real file on disk. Here's what actually got written:

# knitr/pkgdown can only reliably embed images under knitr's own fig.path,
# not an arbitrary absolute path like the tempdir() used above to
# demonstrate an arbitrary save location
preview_path <- knitr::fig_path("png")
dir.create(dirname(preview_path), recursive = TRUE, showWarnings = FALSE)
file.copy(saved_path, preview_path, overwrite = TRUE)
knitr::include_graphics(preview_path)

filename/path can also use @keyword placeholders, expanded the same way xpose::xpose_save() does it:

run_path <- ggsave_xp(dv_vs_ipred(xpdb_ex_pk, quiet = TRUE), filename = "@[e-mail]", path = out_dir)
basename(run_path)

What actually does the saving is itself swappable, via save_fun. The default is ggplot2::ggsave(), but anything sharing its signature works, including third-party wrappers like reportifyr::ggsave_with_metadata(). As a self-contained illustration, so this vignette doesn't need to depend on a third-party package just to demonstrate the idea, here's a save_fun that writes a plain-text note alongside the image:

save_with_note <- function(plot, filename, path = NULL, width, height, note = "", ...) {
  saved <- ggplot2::ggsave(filename = filename, plot = plot, path = path, width = width, height = height, ...)
  writeLines(note, sub("\\.[^.]+$", ".txt", saved))
  saved
}

annotated_path <- ggsave_xp(
  p, filename = "dv_vs_ipred_annotated.png", path = out_dir,
  save_fun = save_with_note, note = "Generated for the Q3 interim analysis."
)

# the .png was written by ggplot2::ggsave() as usual; the .txt is new
readLines(sub("\\.png$", ".txt", annotated_path))

Any function accepting plot/filename/path/width/height (plus whatever else it needs via ...) can be dropped in this way. There's nothing xpose.xtras-specific about save_fun itself.

Automatic application

Everything above can be called explicitly, but it doesn't have to be. Once a default_labs/default_watermark is actually configured, at the option level, as in the examples so far, print.xpose_plot() and ggsave_xp() apply it on their own:

options(
  xpose.xtras.default_labs = list(caption = "DRAFT: do not distribute"),
  xpose.xtras.default_watermark = list(label = "DRAFT")
)

dv_vs_ipred(xpdb_ex_pk, quiet = TRUE)

No apply_default_labs(), no add_watermark(), just an ordinary dv_vs_ipred() call, printed the ordinary way. This is exactly what happens when a plot auto-prints at the console or in a knitted report. It's controlled by the xpose.xtras.auto_apply option, TRUE unless changed. Note that it's the configured default that's applied automatically, not an unconditional one: with default_watermark left unset, auto_apply = TRUE would not stamp a "DRAFT" on every plot on its own. It's purely "apply what was already configured, without asking again."

To turn this off everywhere at once:

options(xpose.xtras.auto_apply = FALSE)

dv_vs_ipred(xpdb_ex_pk, quiet = TRUE)

options(
  xpose.xtras.auto_apply = NULL,
  xpose.xtras.default_labs = NULL,
  xpose.xtras.default_watermark = NULL
)

Or, to opt out for one ggsave_xp() call without touching the option, pass apply_labs = FALSE/apply_watermark = FALSE directly to that call.

Either way, this only ever reaches the session-wide option tier. print() has no way to receive the xpdb a plot was built from, so an xpdb-level default (set via set_default_labs()/set_default_watermark()) still needs apply_default_labs()/add_watermark(), or ggsave_xp()'s xpdb argument, called explicitly. Auto-apply covers the common "one default for the whole session" case, not the per-model one.

Tying it together with session options

Setting several of the options above one at a time is easy to get wrong: a typo in an option name just silently does nothing, since options() doesn't validate names. set_xtras_options() is a small, validated wrapper for the whole xpose.xtras.* family (prefix added automatically), good for pinning a project's defaults once at the top of a script:

set_xtras_options(
  default_labs = list(caption = "DRAFT"),
  default_watermark = list(label = "DRAFT"),
  save_dir = tempdir(),
  save_width = 6,
  save_height = 4
)

# labels and watermark are auto-applied, and save_dir/save_width/save_height
# supply filename's path/width/height: one call, nothing else configured
saved_together <- ggsave_xp(dv_vs_ipred(xpdb_ex_pk, quiet = TRUE), filename = "tied_together.png")
basename(saved_together)

preview_path <- knitr::fig_path("png")
dir.create(dirname(preview_path), recursive = TRUE, showWarnings = FALSE)
file.copy(saved_together, preview_path, overwrite = TRUE)
knitr::include_graphics(preview_path)

The same family also covers a session-wide default theme, gg_theme/xp_theme, picked up automatically the first time an xpose_data object is converted with as_xpdb_x(). A project look can be set once instead of calling xpose::update_themes() on every model:

set_xtras_options(gg_theme = theme_bw)

xpdb_ex_pk %>%
  as_xpdb_x() %>%
  dv_vs_ipred(quiet = TRUE)

get_xtras_option() reports, for a given option and (optionally) a specific xpdb, what's currently set at each tier and which one would win:

xpdb_labelled <- xpdb_x %>%
  set_default_labs(caption = "Model-specific caption")

get_xtras_option("default_labs", xpdb_labelled)

set_xtras_options(
  default_labs = NULL, default_watermark = NULL,
  save_dir = NULL, save_width = NULL, save_height = NULL,
  gg_theme = NULL
)

The full list of recognized options, what each one does, and which ones have an xpdb-level counterpart, is documented on ?set_xtras_options.

xpose.xtras documentation built on Sept. 1, 2026, 5:08 p.m.