Plot Composer – tagging

When multiple plots are combined into a single figure—common in scientific publications—they are often referenced by tags or labels (e.g., “A”, “B”, “C”). While these tags can be added manually, it is much easier to let ggalign handle tagging automatically using the layout_tags() function.

library(ggalign)
#> Loading required package: ggplot2
#> 
#> Attaching package: 'ggalign'
#> The following object is masked from 'package:ggplot2':
#> 
#>     element_polygon

p1 <- ggplot(mtcars) +
    geom_point(aes(mpg, disp))
p2 <- ggplot(mtcars) +
    geom_boxplot(aes(factor(gear), disp))
p3 <- ggplot(mtcars) +
    geom_bar(aes(factor(gear))) +
    facet_wrap(~cyl)

Basic tagging

Set the tags argument in layout_tags() to specify the family of symbols used for tagging plots:

• "1": Arabic numerals (1, 2, 3, …)
• "A": Uppercase Latin letters (A, B, C, …)
• "a": Lowercase Latin letters (a, b, c, …)
• "I": Uppercase Roman numerals (I, II, III, …)
• "i": Lowercase Roman numerals (i, ii, iii, …)

By default, nested layouts receive their own tags:

align_plots(p1, align_plots(p2, p3), ncol = 1) + layout_tags("A")

Suppressing internal tags in nested layouts

To treat a nested layout as a single plot with a single tag, disable its internal tags by setting tags = NULL:

align_plots(p1, align_plots(p2, p3) + layout_tags(NULL), ncol = 1) +
    layout_tags("A")

Multilevel tagging with custom separators

Apply multilevel tagging where the outer layout uses letters and the inner layout uses numbers. You can specify a separator between parent and child tags:

align_plots(
    p1,
    align_plots(p2, p3) + layout_tags(1, sep = ": "),
    ncol = 1
) +
    layout_tags("A")

Adding prefixes and suffixes

You can customize tags by adding a prefix and/or suffix. Note that the parent layout’s prefix and suffix are applied to all plots, including nested layouts:

align_plots(
    p1,
    align_plots(p2, p3) + layout_tags(1, sep = ": "),
    ncol = 1
) +
    layout_tags("A", prefix = "Fig.")

Custom tag sequences

Instead of built-in sequences, you can provide your own tag vector:

align_plots(
    p1,
    align_plots(p2, p3) + layout_tags(1),
    ncol = 1
) +
    layout_tags(c("&", "%"))

Tag appearance and theming

Tags inherit their appearance from the plot’s theme. To modify tag styling for all plots in a layout, use the & operator:

align_plots(
    p1,
    align_plots(p2, p3) + layout_tags(1, sep = ": "),
    ncol = 1
) +
    layout_tags("A", prefix = "Fig.") &
    theme(plot.tag = element_text(color = "red"))

If the plot’s theme does not specify tag styling, the layout’s theme settings from layout_theme() will be used:

align_plots(
    p1,
    align_plots(p2, p3) + layout_tags(1, sep = ": "),
    ncol = 1
) +
    layout_tags("A", prefix = "Fig.") +
    layout_theme(plot.tag = element_text(color = "red"))