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Add Metroglyphs as a Scatterplot

Source: R/geom_metroglyph.R
geom_metroglyph.Rd

The metroglyph geom is used to plot multivariate data as metroglyphs (Anderson 1957; duToit et al. 1986) in a scatterplot.

Usage

geom_metroglyph(
  mapping = NULL,
  data = NULL,
  stat = "identity",
  position = "identity",
  ...,
  cols = character(0L),
  circle.size = 1,
  colour.circle = NULL,
  colour.ray = NULL,
  colour.points = NULL,
  linewidth.circle = 1,
  linewidth.ray = 1,
  lineend = "butt",
  full = TRUE,
  draw.grid = FALSE,
  grid.point.size = 1,
  show.legend = NA,
  legend.glyph.dims = setNames(rep(0.5, length(cols)), cols),
  repel = FALSE,
  repel.control = ggmultiglyph.repel.control(),
  inherit.aes = TRUE
)

Arguments

mapping

Set of aesthetic mappings created by aes(). If specified and inherit.aes = TRUE (the default), it is combined with the default mapping at the top level of the plot. You must supply mapping if there is no plot mapping.

data

The data to be displayed in this layer. There are three options:

If NULL, the default, the data is inherited from the plot data as specified in the call to ggplot().

A data.frame, or other object, will override the plot data. All objects will be fortified to produce a data frame. See fortify() for which variables will be created.

A function will be called with a single argument, the plot data. The return value must be a data.frame, and will be used as the layer data. A function can be created from a formula (e.g. ~ head(.x, 10)).

stat

The statistical transformation to use on the data for this layer. When using a geom_*() function to construct a layer, the stat argument can be used to override the default coupling between geoms and stats. The stat argument accepts the following:

  • A Stat ggproto subclass, for example StatCount.

  • A string naming the stat. To give the stat as a string, strip the function name of the stat_ prefix. For example, to use stat_count(), give the stat as "count".

  • For more information and other ways to specify the stat, see the layer stat documentation.

position

A position adjustment to use on the data for this layer. This can be used in various ways, including to prevent overplotting and improving the display. The position argument accepts the following:

  • The result of calling a position function, such as position_jitter(). This method allows for passing extra arguments to the position.

  • A string naming the position adjustment. To give the position as a string, strip the function name of the position_ prefix. For example, to use position_jitter(), give the position as "jitter".

  • For more information and other ways to specify the position, see the layer position documentation.

...

Other arguments passed on to layer(). These are often aesthetics, used to set an aesthetic to a fixed value, like colour = "green" or size = 3. They may also be parameters to the paired geom/stat.

cols

A character vector containing the names of at least two columns specifying the variables to be plotted in the glyphs. The selected columns must be either numeric or factor variables.

circle.size

The size of the central circle (radius).

colour.circle

The colour of circles.

colour.ray

The colour of rays.

colour.points

The colour of grid points.

linewidth.circle

The circle line width.

linewidth.ray

The ray line width.

lineend

The line end style for the rays. Either "round", "butt" or "square".

full

logical. If TRUE, full star glyphs (360°) are plotted, otherwise half star glyphs (180°) are plotted.

draw.grid

logical. If TRUE, grid points are plotted along the rays if all the variables specified in cols are an ordered factor. Default is FALSE.

grid.point.size

The size of the grid points in native units.

show.legend

logical. Should this layer be included in the legends? NA, the default, includes if any aesthetics are mapped. FALSE never includes, and TRUE always includes. It can also be a named logical vector to finely select the aesthetics to display. To include legend keys for all levels, even when no data exists, use TRUE. If NA, all levels are shown in legend, but unobserved levels are omitted.

legend.glyph.dims

The dimensions of the legend glyph plot. Can be a numeric vector of unit length (where all the dimensions will have same value) or a numeric vector of same length as "cols" with the "cols" as names.

repel

logical. If TRUE, the glyphs are repel away from each other to avoid overlaps. Default is FALSE.

repel.control

A list of control settings for the repel algorithm. Ignored if repel = FALSE. See ggmultiglyph.repel.control for details on the various control parameters.

inherit.aes

If FALSE, overrides the default aesthetics, rather than combining with them. This is most useful for helper functions that define both data and aesthetics and shouldn't inherit behaviour from the default plot specification, e.g. annotation_borders().

Value

A geom layer.

Aesthetics

geom_metroglyph() understands the following aesthetics (required aesthetics are in bold):

  • x

  • y

  • alpha

  • colour

  • fill

  • group

  • circle.size

See vignette("ggplot2-specs", package = "ggplot2") for further details on setting these aesthetics.

The following additional aesthetics are considered if repel = TRUE:

  • point.size

  • segment.linetype

  • segment.colour

  • segment.size

  • segment.alpha

  • segment.curvature

  • segment.angle

  • segment.ncp

  • segment.shape

  • segment.square

  • segment.squareShape

  • segment.inflect

  • segment.debug

See ggrepel examples page for further details on setting these aesthetics.

References

Anderson E (1957). “A semigraphical method for the analysis of complex problems.” Proceedings of the National Academy of Sciences of the United States of America, 43(10), 923.

duToit SHC, Steyn AGW, Stumpf RH (1986). Graphical Exploratory Data Analysis, Springer Texts in Statistics. Springer-Verlag, New York. ISBN 978-1-4612-9371-2.

See also

metroglyphGrob

Other geoms: geom_dotglyph(), geom_pieglyph(), geom_profileglyph(), geom_starglyph(), geom_tileglyph()

Examples



library(ggplot2)

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Prepare the data ----
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

# Variables to map to glyphs
zs <- c("hp", "drat", "wt", "qsec", "vs", "am", "gear", "carb")

# Keep a copy of the original data
mtcars_fct <- mtcars

# Scaled numeric data
mtcars[zs] <- lapply(mtcars[zs], scales::rescale)

mtcars$cyl <- factor(mtcars$cyl)
mtcars$lab <- row.names(mtcars)

# Ordered factor data
mtcars_fct[zs[1:3]] <-
  lapply(mtcars_fct[zs[1:3]], function(x)
    ordered(cut(x, breaks = 3,
                labels = c("low", "medium", "high"))))

mtcars_fct[zs[4:8]] <-
  lapply(mtcars_fct[zs[4:8]], function(x)
    ordered(cut(x, breaks = 4,
                labels = c("tiny", "small", "medium", "large"))))

mtcars_fct$cyl <- factor(mtcars_fct$cyl)
mtcars_fct$lab <- row.names(mtcars_fct)

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Mapped colour ----
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

ggplot(data = mtcars) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl),
                  cols = zs, circle.size = 3, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 10, alpha =  0.8) +
  ylim(c(-0, 550))


ggplot(data = mtcars) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl),
                  cols = zs, circle.size = 3, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2, fill = "gray30",
                  size = 10, alpha =  0.8) +
  ylim(c(-0, 550))


ggplot(data = mtcars) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl),
                  cols = zs, circle.size = 3, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  full = FALSE,
                  size = 10, alpha =  0.8) +
  ylim(c(-0, 550))


ggplot(data = mtcars) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl),
                  cols = zs, circle.size = 3, colour.ray = NULL,
                  full = FALSE,
                  linewidth.circle = 2, linewidth.ray = 2, fill = "gray30",
                  size = 10, alpha =  0.8) +
  ylim(c(-0, 550))


# \donttest{
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Mapped colour + fill ----
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

ggplot(data = mtcars) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl, fill = cyl),
                  cols = zs, circle.size = 3, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 10, alpha =  0.8) +
  ylim(c(-0, 550))


ggplot(data = mtcars) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl, fill = cyl),
                  cols = zs, circle.size = 3, colour.ray = NULL,
                  full = FALSE,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 10, alpha =  0.8) +
  ylim(c(-0, 550))


#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Mapped fill ----
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

ggplot(data = mtcars) +
  geom_metroglyph(aes(x = mpg, y = disp, fill = cyl),
                  cols = zs, circle.size = 3, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 10, alpha =  0.8) +
  ylim(c(-0, 550))


ggplot(data = mtcars) +
  geom_metroglyph(aes(x = mpg, y = disp, fill = cyl),
                  cols = zs, circle.size = 3, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  colour.circle = "transparent",
                  size = 10, alpha =  0.8) +
  ylim(c(-0, 550))


ggplot(data = mtcars) +
  geom_metroglyph(aes(x = mpg, y = disp, fill = cyl),
                  cols = zs, circle.size = 3, colour.ray = NULL,
                  full = FALSE,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 10, alpha =  0.8) +
  ylim(c(-0, 550))


ggplot(data = mtcars) +
  geom_metroglyph(aes(x = mpg, y = disp, fill = cyl),
                  cols = zs, circle.size = 3, colour.ray = NULL,
                  full = FALSE, colour.circle = "transparent",
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 10, alpha =  0.8) +
  ylim(c(-0, 550))


#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Rays with multivariate colours ----
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

ggplot(data = mtcars) +
  geom_metroglyph(aes(x = mpg, y = disp),
                  cols = zs, circle.size = 3,
                  linewidth.circle = 0, linewidth.ray = 2,
                  colour.circle = "transparent", fill = "gray",
                  colour.ray = RColorBrewer::brewer.pal(8, "Dark2"),
                  size = 10, alpha =  0.8) +
  ylim(c(-0, 550))


ggplot(data = mtcars) +
  geom_metroglyph(aes(x = mpg, y = disp),
                  cols = zs, circle.size = 3,
                  linewidth.circle = 0, linewidth.ray = 2,
                  colour.circle = "transparent", fill = "gray",
                  colour.ray = RColorBrewer::brewer.pal(8, "Dark2"),
                  size = 10, alpha =  0.8, full = FALSE) +
  ylim(c(-0, 550))


#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Faceted ----
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

ggplot(data = mtcars) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl),
                  cols = zs, circle.size = 3, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 10, alpha =  0.8) +
  ylim(c(-0, 550)) +
  facet_grid(. ~ cyl)


ggplot(data = mtcars) +
  geom_metroglyph(aes(x = mpg, y = disp, fill = cyl),
                  cols = zs, circle.size = 3, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 10, alpha =  0.8) +
  ylim(c(-0, 550)) +
  facet_grid(. ~ cyl)


#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Repel glyphs ----
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

ggplot(data = mtcars) +
  geom_point(aes(x = mpg, y = disp, colour = cyl)) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl),
                  cols = zs, circle.size = 3, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 10, alpha =  1, repel = TRUE) +
  ylim(c(-0, 550))
#> Warning: 14 glyphs have too many overlaps.
#> Consider increasing "max.overlaps"


ggplot(data = mtcars) +
  geom_point(aes(x = mpg, y = disp, colour = cyl)) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl, fill = cyl),
                  cols = zs, circle.size = 3, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  colour.circle = "transparent",
                  size = 10, alpha =  1, repel = TRUE) +
  ylim(c(-0, 550))
#> Warning: 14 glyphs have too many overlaps.
#> Consider increasing "max.overlaps"


ggplot(data = mtcars) +
  geom_point(aes(x = mpg, y = disp)) +
  geom_metroglyph(aes(x = mpg, y = disp),
                  cols = zs, circle.size = 3,
                  linewidth.circle = 0, linewidth.ray = 2,
                  colour.circle = "transparent", fill = "gray",
                  colour.ray = RColorBrewer::brewer.pal(8, "Dark2"),
                  size = 10, alpha =  1, repel = TRUE) +
  ylim(c(-0, 550))
#> Warning: 11 glyphs have too many overlaps.
#> Consider increasing "max.overlaps"


#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# With grid points ----
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

ggplot(data = mtcars_fct) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl),
                  cols = zs, circle.size = 3, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 2.5, alpha =  0.8,
                  draw.grid = TRUE, grid.point.size = 5) +
  ylim(c(-0, 550))


ggplot(data = mtcars_fct) +
  geom_metroglyph(aes(x = mpg, y = disp, fill = cyl),
                  cols = zs, circle.size = 3, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 2.5, alpha =  0.8,
                  draw.grid = TRUE, grid.point.size = 5) +
  ylim(c(-0, 550))


ggplot(data = mtcars_fct) +
  geom_metroglyph(aes(x = mpg, y = disp),
                  cols = zs, circle.size = 3,
                  linewidth.circle = 0, linewidth.ray = 2,
                  colour.circle = "transparent", fill = "gray",
                  colour.ray = RColorBrewer::brewer.pal(8, "Dark2"),
                  size = 2.5, alpha =  0.8,
                  draw.grid = TRUE, grid.point.size = 5) +
  ylim(c(-0, 550))


#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Legend options ----
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

# Default legend/guide
ggplot(data = mtcars) +
  geom_point(aes(x = mpg, y = disp, colour = cyl)) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl),
                  cols = zs, circle.size = 2, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 5, alpha =  1, repel = TRUE) +
  ylim(c(-0, 550))


# Theme modifications for legend
legend_theme <-
  theme_bw(base_size = 7.5) +
  theme(legend.direction = "vertical",
        legend.box = "horizontal",
        legend.position = "bottom",
        legend.text = element_text(margin = margin(l = 7)),
        legend.key.height = unit(1.5, 'lines'))

# Glyph variable-wise legends
ggplot(data = mtcars) +
  geom_point(aes(x = mpg, y = disp, colour = cyl)) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl),
                  cols = zs, circle.size = 1, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 5, alpha =  1, repel = TRUE) +
  ylim(c(-0, 550)) +
  scale_z_continuous(z = zs) +
  guide_z_order(z = zs, default_aes = "colour") +
  legend_theme


# Modifying the `legend.glyph.dims`
zavg <- # Scaled average of the variables
  apply(mtcars[, zs], 2,
        function(x) {
          scales::rescale(mean(x),
                          from = range(x), # same range as in scale_z_continuous
                          to = c(0, 1))
        })
zavg
#>        hp      drat        wt      qsec        vs        am      gear      carb 
#> 0.3345848 0.3855127 0.4357581 0.3986607 0.4375000 0.4062500 0.3437500 0.2589286 

ggplot(data = mtcars) +
  geom_point(aes(x = mpg, y = disp, colour = cyl)) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl),
                  cols = zs, circle.size = 2, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 5, alpha =  1, repel = TRUE) +
  ylim(c(-0, 550)) +
  xlim(c(8, 35))
#> Warning: 2 glyphs have too many overlaps.
#> Consider increasing "max.overlaps"


ggplot(data = mtcars) +
  geom_point(aes(x = mpg, y = disp, colour = cyl)) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl),
                  cols = zs, circle.size = 1, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 5, alpha =  1, repel = TRUE) +
  ylim(c(-0, 550)) +
  scale_z_continuous(z = zs) +
  guide_z_order(z = zs, default_aes = "colour")  +
  legend_theme


# Using custom guide
# metroglyphGrob
guide_metrogrob <- metroglyphGrob(
  z = c(0.24, 0.3, 0.8, 1.4, 0.6, 0.33, 0.6, 0.25) * 0.5,
  size = 25)
# Add labels to metroglyphGrob
guide_metrogrob <-
  addlabel.glyphGrob(grob = guide_metrogrob, label = zs,
                     push = 1, segment = FALSE)

# Another version
guide_metrogrob2 <- metroglyphGrob(
  z = rep(0.3, length(zs)),
  size = 25)
guide_metrogrob2 <-
  addlabel.glyphGrob(grob = guide_metrogrob2, label = zs,
                     push = 1, segment = FALSE)

ggplot(data = mtcars) +
  geom_point(aes(x = mpg, y = disp, colour = cyl)) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl),
                  cols = zs, circle.size = 1, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 5, alpha =  1, repel = TRUE) +
  ylim(c(-0, 550)) +
  guides(colour = guide_legend(order = 1, position = "right"),
         custom = guide_custom(guide_metrogrob,
                               width = unit(0.1, "npc"),
                               height = unit(0.1, "npc"),
                               position = "bottom",
                               theme = theme(legend.margin = margin(t = 40, b = 30))))


ggplot(data = mtcars) +
  geom_point(aes(x = mpg, y = disp, colour = cyl)) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl),
                  cols = zs, circle.size = 1, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 5, alpha =  1, repel = TRUE) +
  ylim(c(-0, 550)) +
  guides(colour = guide_legend(order = 1, position = "right"),
         custom = guide_custom(guide_metrogrob2,
                               width = unit(0.1, "npc"),
                               height = unit(0.1, "npc"),
                               position = "bottom",
                               theme = theme(legend.margin = margin(t = 30, b = 30))))


# Legend in plots with grid points

z_grid <- c(hp = 3, drat = 3, wt = 2,
            qsec = 2, vs = 3, am = 4,
            gear = 2, carb = 3)

ggplot(data = mtcars_fct) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl),
                  cols = zs, circle.size = 1, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 1.5, alpha =  0.8,
                  draw.grid = TRUE, grid.point.size = 5) +
  ylim(c(-0, 550))


ggplot(data = mtcars_fct) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl),
                  cols = zs, circle.size = 1, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 1.5, alpha =  0.8,
                  draw.grid = TRUE, grid.point.size = 5) +
  ylim(c(-0, 550)) +
  scale_z_discrete(z = zs) +
  guide_z_order(z = zs, default_aes = "fill") +
  legend_theme


ggplot(data = mtcars_fct) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl),
                  cols = zs, circle.size = 1, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 1.5, alpha =  0.8,
                  draw.grid = TRUE, grid.point.size = 5,
                  legend.glyph.dims = z_grid) +
  ylim(c(-0, 550))


ggplot(data = mtcars_fct) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl),
                  cols = zs, circle.size = 1, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 1.5, alpha =  0.8,
                  draw.grid = TRUE, grid.point.size = 5,
                  legend.glyph.dims = z_grid) +
  ylim(c(-0, 550)) +
  scale_z_discrete(z = zs) +
  guide_z_order(z = zs, default_aes = "fill") +
  legend_theme


# metroglyphGrob with grid levels

z_grid_levels <- lapply(z_grid, function(x) 1:x)

guide_metrogrob_grid <-
  metroglyphGrob(z = z_grid,
                size = 2.5, draw.grid = TRUE, circle.size = 2,
                grid.levels = z_grid_levels,
                grid.point.size = 0.1)

guide_metrogrob_grid <-
  addlabel.glyphGrob(grob = guide_metrogrob_grid, label = zs,
                     push = 1, segment = FALSE)

# Another version
guide_metrogrob_grid2 <-
  metroglyphGrob(z = rep(3, length(z_grid)),
                size = 2.5, draw.grid = TRUE, circle.size = 2,
                grid.levels = replicate(8, 1:3,
                                        simplify = FALSE),
                grid.point.size = 0.1)
guide_metrogrob_grid2 <-
  addlabel.glyphGrob(grob = guide_metrogrob_grid2, label = zs,
                     push = 1, segment = FALSE)

ggplot(data = mtcars_fct) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl),
                  cols = zs, circle.size = 1, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 1.5, alpha =  0.8,
                  draw.grid = TRUE, grid.point.size = 5,
                  legend.glyph.dims = z_grid) +
  ylim(c(-0, 550)) +
  guides(fill = guide_legend(order = 1, position = "right"),
         custom = guide_custom(guide_metrogrob_grid,
                               width = unit(0.1, "npc"),
                               height = unit(0.1, "npc"),
                               position = "bottom",
                               theme = theme(legend.margin = margin(t = 20, b = 30))))


ggplot(data = mtcars_fct) +
  geom_metroglyph(aes(x = mpg, y = disp, colour = cyl),
                  cols = zs, circle.size = 1, colour.ray = NULL,
                  linewidth.circle = 2, linewidth.ray = 2,
                  size = 1.5, alpha =  0.8,
                  draw.grid = TRUE, grid.point.size = 5,
                  legend.glyph.dims = z_grid) +
  ylim(c(-0, 550)) +
  guides(fill = guide_legend(order = 1, position = "right"),
         custom = guide_custom(guide_metrogrob_grid2,
                               width = unit(0.1, "npc"),
                               height = unit(0.1, "npc"),
                               position = "bottom",
                               theme = theme(legend.margin = margin(t = 20, b = 30))))

# }