Automatically determine prefix and suffix from tags

[thomas-neitmann]

I have implemented an automatic detection of the tag_prefix and tag_suffix from the tag_levels as described in #169. It works like this:

1. Look whether tag_levels contains one of the supported tags using grepl()
2. If it does and tag_levels is longer than 1 character then find the index of the supported tag inside tag_levels
3. Use anything that comes before this index as tag_prefix
4. Use anything that comes after this index as tag_suffix

Some examples:

• In the case of tag_levels = "A", tag_prefix and tag_suffix are left blank.
• In case of tag_levels = "[A", tag_prefix is set to "]" and tag_suffix is left blank.
• In case of tag_levels = "A}", tag_prefix is left blank and tag_suffix is set to "}".
• In case of tag_levels = "(A)", tag_prefix is is set to "(" and tag_suffix is set to ")".

Importantly, in the current implentation the automatic detection of the prefix is not "activated" when tag_prefix is set. The same is true for the suffix is tag_suffix is set.

library(ggplot2)
p1 <- ggplot(mtcars, aes(mpg, hp)) + geom_point()
p2 <- ggplot(mtcars, aes(wt)) + geom_histogram()

p1 + p2 + plot_annotation(tag_levels = "1")

p1 + p2 + plot_annotation(tag_levels = "A)")

p1 + p2 + plot_annotation(tag_levels = "[I]")

p1 + p2 + plot_annotation(tag_levels = "{a")

p1 + p2 + plot_annotation(tag_levels = "(A)", tag_prefix = "[", tag_suffix = "]")

[thomasp85]

On second thought, I think the best approach is something incorporating glue. Your current checks for which formats to use will fail if prefix or suffix contains any of the recognised tokens