Marquee guide

[teunbrand]

Hi Thomas,

This is my proposal for a marquee guide.
Instead of going into details, I'll render the examples which are hopefully somewhat self-expanatory.
Please let me know if you'd wish to change some things.

library(ggplot2)
library(marquee)
# A standard plot
base <- ggplot(mpg, aes(displ, hwy)) +
  geom_point()

# Using key glyphs
base + aes(shape = drv) +
  scale_shape_discrete(
    # Same as using <<1>>, <<2>> and <<3>>,
    # or ![](1), ![](2) and ![](3)
    # or ![](4), ![](f) and ![](r)
    name = "Cars with four wheel <<4>>, forward <<f>> or reverse <<r>> drive.",
    guide = "marquee"
  )

# Recolouring text
base <- base +
  aes(colour = drv) +
  labs(
    colour = "Cars with {.4 four wheel}, {.f forward} or {.r reverse} drive."
  )
base + guides(colour = "marquee")

# Adjust display of labels
st <- style(weight = "bold", italic = TRUE, background = NA)
base + guides(colour = guide_marquee(style = st))

# Using background instead of text colour by setting it to NULL
st <- style(color = "black", background = NULL)
base + guides(colour = guide_marquee(style = st))

# Customising style of each label through style sets
# Note: tag names must be universal per `vctrs::vec_as_names` and
# prefixed with `lab_`.
st <- classic_style()
st <- modify_style(st, tag = "lab_f", background = NULL, color = "black")
st <- modify_style(st, tag = "lab_r", border_size = trbl(1),
                   color = "black", background = NA)
base + guides(colour = guide_marquee(style = st))

# Alternatively:
base + guides(colour = "marquee") +
  theme(plot.subtitle = element_marquee(style = st))

# Splicing in labels
base + aes(colour = class) +
  labs(colour = "Cars including !!2 and !!6 vehicles") +
  guides(colour = "marquee")

# Using automatic detection
base + aes(colour = class) +
  labs(colour = "Cars including suv and minivan vehicles") +
  guides(colour = guide_marquee(detect = TRUE))

# Automatic detection is not always a good idea
base +
  labs(colour = "Kerfuffles 4 the riffraff from frankfurt") +
  guides(colour = guide_marquee(detect = TRUE))

^{Created on 2024-06-06 with reprex v2.1.0}

[thomasp85]

This looks very promising. Some thoughts:

• I think the automatic detection can focus on whole words so as to avoid the last example. I can't see when it would ever be useful not want it to detect full words
• breaks can include spaces while marquee classes cannot. How is this handled?
• How can this be combined with a regular legend? If possible at all?
• It's not clear how the splicing in of labels happens. What are 2 and 6 referring to?

[teunbrand]

I think the automatic detection can focus on whole words so as to avoid the last example. I can't see when it would ever be useful not want it to detect full words

I'll look into finding the right regex incantation for this.

breaks can include spaces while marquee classes cannot. How is this handled?

Through the repair = "universal" in vec_as_names() for class names. It ensures the tag is both syntactic and unique.

x <- "I'm displaying spaces."
tolower(vctrs::vec_as_names(x, repair = "universal", quiet = TRUE))
#> [1] "i.m.displaying.spaces."

^{Created on 2024-06-07 with reprex v2.1.0}

How can this be combined with a regular legend? If possible at all?

It cannot, I don't think you can have >1 guide per aesthetic in ggplot2.
You can hack it of course by using a guide for a different aesthetic with the same mapping and using override.aes to emulate the original aesthetic.

It's not clear how the splicing in of labels happens. What are 2 and 6 referring to?

Using !!n will insert the n^th label, so !!2 and !!6 will insert the 2^nd and 6^th label.
It would be the same as "Cars including !!compact and !!subcompact vehicles". Perhaps the example should mix the two ways to showcase them both. This pattern is included in the 'text formatting' section of the docs.

[thomasp85]

Ok, let's merge this in and take it for a spin. Can you add a topic to the pkgdown site so that doesn't fail

[teunbrand]

Gotcha

[thomasp85]

Thank you