Auto-Adjust ggplot2 Plot Width for Facet Secondary Labels

Yes — you can automate margin/width adjustments so ggplot2 won’t clip external secondary‑axis labels. In r ggplot2 the usual patterns are: (A) measure the text/grob extents and set theme(plot.margin) or ggsave width per plot, (B) convert the ggplot to a gtable and add a right column + label grob, or © use ggh4x facet options (axes=‘all’ / axes=‘margins’ and force_panelsizes) to avoid external labels entirely. Below I give practical, copy‑pasteable patterns for each approach plus pitfalls and tips.

Contents

• How ggplot2 clipping, coord_cartesian and plot.margin interact
• Programmatic approach 1 — compute text/grob widths and set theme(plot.margin)
• Programmatic approach 2 — compute extra width and save with adjusted ggsave width / device
• Programmatic approach 3 — gtable: add a right column and attach label grobs (no manual margin tuning)
• ggh4x alternatives: use per‑facet axes and force_panelsizes
• Practical tips, gotchas and recommended pattern for purrr::map workflows
• Sources
• Conclusion

How ggplot2 clipping, coord_cartesian and plot.margin interact

coord_cartesian(clip = “off”) stops ggplot2 from clipping grobs at the panel box, but it does not automatically expand the outer plot area (the gtable columns/rows that surround the panels). If the outer right margin isn’t large enough the device will still cut off text even though the panel clip is off — that’s why theme(plot.margin) or adding space to the gtable is necessary. The ggplot2 theme system and gtable/grid low‑level API are the two places to act: either increase the right margin (easy) or permanently add a new right column to the plot gtable and attach the label grob there (robust). See ggplot2 theme docs for margin usage and related discussions about clip behavior and facets: https://ggplot2.tidyverse.org/reference/element.html and https://github.com/tidyverse/ggplot2/issues/2350.

Programmatic approach 1 — compute text/grob widths and set theme(plot.margin)

Idea: before saving each plot compute how wide your external labels will be (using grid::textGrob + grobWidth + convertX) and set theme(plot.margin) accordingly. This is the easiest to integrate into a purrr::map workflow.

Key points:

• Match the textGrob gp (fontsize, family, face) to what geom_text will use (or to theme text settings).
• Add a small padding (0.2–0.4 cm) to avoid tight fits.
• If you save at a different device/dpi than your interactive session, compute widths on the target device (see notes below).

Example (simple helper + usage):

library(ggplot2)
library(grid)

# helper: width in cm for a single string (match fontsize to geom_text)
grob_width_cm <- function(text, fontsize = 10, fontfamily = "", fontface = "plain") {
 tg <- textGrob(text, gp = gpar(fontsize = fontsize, fontfamily = fontfamily, fontface = fontface))
 convertX(grobWidth(tg), "cm", valueOnly = TRUE)
}

# usage inside a per-plot routine
make_plot_with_margin <- function(p, labels, fontsize = 10, pad_cm = 0.3) {
 # labels: character vector of the external strings for this plot
 widths <- vapply(labels, grob_width_cm, numeric(1), fontsize = fontsize)
 right_cm <- max(widths, na.rm = TRUE) + pad_cm
 p + coord_cartesian(clip = "off") +
 theme(plot.margin = margin(0.2, right_cm, 0.2, 0.5, unit = "cm"))
}

If you call make_plot_with_margin inside purrr::map you get a per‑plot margin that adapts to the label widths, with no manual tuning.

Sources and similar examples: see how people compute grobWidth and set plot.margin on StackOverflow and the ggplot2 element docs: https://stackoverflow.com/questions/72434047/calculate-the-width-of-a-geom-text-in-ggplot2 and https://ggplot2.tidyverse.org/reference/element.html.

Programmatic approach 2 — compute extra width and save with adjusted ggsave width / device

If you prefer to keep the plot object unchanged and instead change the saved figure width, measure the label width and add that to your base width when calling ggsave (or when opening png/pdf device). This is great when you have a fixed per‑panel width and want output files sized correctly.

Pattern:

1. Build the ggplot object p (with coord_cartesian(clip = “off”) optionally).
2. Compute required extra width in inches from textGrob widths.
3. Save with ggsave(width = base_width + extra_in).

Example:

library(grid)

# compute extra inches needed (match fontsize)
extra_in_needed <- function(labels, fontsize = 10, pad_in = 0.12) {
 widths_cm <- vapply(labels, function(lbl) {
 convertX(grobWidth(textGrob(lbl, gp = gpar(fontsize = fontsize))), "cm", valueOnly = TRUE)
 }, numeric(1))
 max(widths_cm, na.rm = TRUE) / 2.54 + pad_in
}

# save per-plot
base_width_in <- 7 # your normal width for multi-column plots
extra_in <- extra_in_needed(my_labels, fontsize = 10)
ggsave("plot.png", plot = p, width = base_width_in + extra_in, height = 5, units = "in", dpi = 300)

Heads up: convertX/grobWidth are most accurate when the unit system matches the final device (font metrics vary by device/dpi). For foolproof results open the target device (png/pdf) first, compute grob widths, then write the plot (or use the gtable method below which embeds the grob directly).

See Andrew Heiss’s long‑label notes for a similar workflow: https://www.andrewheiss.com/blog/2022/06/23/long-labels-ggplot/.

Programmatic approach 3 — gtable: add a right column and attach label grobs (no manual margin tuning)

This is the most robust solution: convert ggplot to a gtable, add an extra column sized to the label grob, and then insert your label grob(s) in that column spanning the panel rows. Because the gtable itself now contains the extra space and the grob, nothing is clipped and you don’t rely on plot.margin.

Example (full pattern):

library(ggplot2)
library(gtable)
library(grid)

# p: ggplot object (you can keep geom_text/geom_segment calls OR skip them and add labels via grob)
p <- p + coord_cartesian(clip = "off") # keep panel clipping off

# build grob and compute width
label_text <- "My long external label"
tg <- textGrob(label_text, gp = gpar(fontsize = 10), x = unit(0, "npc"), y = unit(0.5, "npc"), just = "left")
w_cm <- convertX(grobWidth(tg), "cm", valueOnly = TRUE)

# get gtable and add a right column
g <- ggplotGrob(p)
g <- gtable_add_cols(g, unit(w_cm + 0.3, "cm"), pos = ncol(g)) # add column at the far right

# find panel extents and add the text grob into the new right column
panel_rows <- which(g$layout$name == "panel")
top_row <- min(g$layout$t[panel_rows])
bottom_row <- max(g$layout$b[panel_rows])

g <- gtable_add_grob(g, list(tg), t = top_row, l = ncol(g), b = bottom_row, r = ncol(g), clip = "off")

# draw or save (use a device sized to the gtable or draw to a file)
grid.newpage()
grid.draw(g)

Notes:

• If you already draw geom_text at x = I(1.21) you can remove it from the ggplot and instead create the text grob above (this avoids double drawing).
• For multi‑line or many labels build a single textGrob with newline separators or create multiple grobs positioned at desired y positions.
• To save the gtable to file with exact sizing, compute the gtable width (sum of its column widths) and open a device sized to that; see code below to compute total width in inches:

total_w_in <- sum(convertWidth(do.call(unit.c, as.list(g$widths)), "in", valueOnly = TRUE))
png("out.png", width = total_w_in, height = 5, units = "in", res = 300)
grid.draw(g)
dev.off()

This approach comes from gtable/grid patterns widely used in the ggplot community: https://cran.r-project.org/web/packages/gridExtra/vignettes/gtable.html and the StackOverflow threads demonstrating gtable_add_cols for facet label margins: https://stackoverflow.com/questions/66101250/turn-off-clipping-of-facet-labels.

ggh4x alternatives: use per‑facet axes and force_panelsizes

Before you go deep into grob math, consider whether ggh4x can remove the need for external labels. ggh4x::facet_wrap2 has options (axes = “all” or axes = “margins”) that draw axes and strips outside panels in ways ggplot2 doesn’t by default; combining this with force_panelsizes() lets you control per-panel size so plots with fewer columns don’t suddenly need larger outer margins.

Example:

library(ggh4x)

p + facet_wrap2(vars(qc, site), nrow = unique(.data$nqc), axes = "all", strip = strip_nested()) +
 force_panelsizes(rows = unit(4, "cm"), cols = unit(3, "cm"))

Using axes=‘all’ often means you can put numeric labels on the secondary axis inside each facet or use facet-level axis drawing instead of external geom_text. See the ggh4x facets guide: https://teunbrand.github.io/ggh4x/articles/Facets.html and the reference for facet_wrap2: https://teunbrand.github.io/ggh4x/reference/facet_wrap2.html.

Practical tips, gotchas and recommended pattern for purrr::map workflows

• Where to measure: unit widths depend on device font metrics. If you need pixel‑perfect results, measure grobWidth after opening a device with the same DPI and font environment you’ll use for saving. For batch runs open a png/pdf to a tempfile to measure, then save final plot with the computed sizes.
• Matching font settings: make the textGrob gp (fontsize, family, face) match the geom_text call or the theme element. If you rely on theme defaults, you can query them (e.g., theme_get()) and use those values.
• Consistency across many plots: to keep a uniform column across many analyte plots, compute the maximum external label width across all analytes and apply that single right margin/width to every plot. That avoids changes in visual width between pages.
• Avoid fragile numeric constants: prefer pad (0.2–0.4 cm) vs hardcoded 1.2 or 1.5, and test at your final resolution (dpi).
• If you need labels aligned to specific rows/panels, compute panel positions in the gtable (g$layout where name == “panel”) and place the grob exactly where you want.
• If you’re comfortable with grid/gtable, the add‑column pattern is robust and reproducible across devices; if you want simpler code, measuring width and changing plot.margin is usually enough.
• For a one‑time print-quality batch, adjusting ggsave width per plot tends to be fastest.

Helpful references and examples (discussed above): https://stackoverflow.com/questions/9690648/avoid-clipping-of-points-along-axis-in-ggplot, https://stackoverflow.com/questions/13867325/get-width-of-plot-area-in-ggplot2, https://www.andrewheiss.com/blog/2022/06/23/long-labels-ggplot/.

Sources

• https://ggplot2.tidyverse.org/reference/element.html
• https://github.com/tidyverse/ggplot2/issues/2350
• https://stackoverflow.com/questions/9690648/avoid-clipping-of-points-along-axis-in-ggplot
• https://stackoverflow.com/questions/72434047/calculate-the-width-of-a-geom-text-in-ggplot2
• https://stackoverflow.com/questions/66101250/turn-off-clipping-of-facet-labels
• https://cran.r-project.org/web/packages/gridExtra/vignettes/gtable.html
• https://www.andrewheiss.com/blog/2022/06/23/long-labels-ggplot/
• https://teunbrand.github.io/ggh4x/articles/Facets.html
• https://teunbrand.github.io/ggh4x/reference/facet_wrap2.html

Conclusion

Automating right‑side space for external secondary‑axis labels in ggplot2 is doable and reliable: measure the label/grob extent and either (1) set theme(plot.margin) per plot, (2) increase the saved figure width when calling ggsave, or (3) convert the plot to a gtable and add a dedicated right column for the label grob (most robust). If you prefer avoiding external grobs entirely, ggh4x::facet_wrap2 (axes=‘all’ / force_panelsizes) often eliminates the problem. Pick the approach that best fits your pipeline: quick margin calc for simplicity, ggsave width for file sizing, or gtable insertion for full control.