The ggcolormeter package provides a single function guide_colormeter(), which is a ggplot2 color/fill legend guide extension in the style of a dashboard meter.

Installation

install.packages("ggcolormeter")
# or
remotes::install_github("yjunechoe/ggcolormeter")

Simple usage

library(ggplot2)
library(ggcolormeter)

theme_set(theme_classic())

p <- ggplot(mtcars, aes(drat, hp)) +
  geom_point(aes(color = mpg))

p +
  scale_color_viridis_c(
    option = "inferno",
    breaks = scales::breaks_pretty(10),
    guide = guide_colormeter()
  )

Colormeter guide theme components

The colormeter guide has argument families for styling 5 distinct components of the guide:

Size and aspect
Arc
Label
Dashboard
Frame

Position of these theme elements is relative to the guide-internal coordinate system, which you can inspect with the debug = TRUE argument.

1) Size and aspect

The colormeter legend is a bit pecular in that its size doesn’t expand with more keys: the colormeter has a fixed size and shape, and its elements are packed inside it.

You can primarily control the size of the legend with legend_size and aspect.ratio

p +
  scale_color_viridis_c(
    option = "inferno",
    breaks = scales::breaks_pretty(10),
    guide = guide_colormeter(
      legend_size = unit(3, "cm"),
      aspect.ratio = .8
    )
  )

Note that the usual legend background is still present and different from the dashboard circle:

p +
  scale_color_viridis_c(
    option = "inferno",
    breaks = scales::breaks_pretty(10),
    guide = guide_colormeter(
      legend_size = unit(3, "cm"),
      aspect.ratio = .8
    )
  ) +
  theme(legend.background = element_rect(color = "red", fill = "pink"))

Most of the time you’d want to remove this legend background, as the dashboard serves that purpose:

p +
  scale_color_viridis_c(
    option = "inferno",
    breaks = scales::breaks_pretty(10),
    guide = guide_colormeter(
    )
  ) +
  theme(
    legend.position = c(.85, .75),
    legend.background = element_blank()
  )

2) Arc

formals(guide_colormeter)[grepl("arc", names(formals(guide_colormeter)))]
#> $arc_range
#> c(-4/7 * pi, 4/7 * pi)
#> 
#> $arc_radius
#> [1] 1
#> 
#> $arc_width
#> arc_radius/4
#> 
#> $arc_gap
#> arc_radius/5
#> 
#> $arc_rounding
#> [1] 0

Non-positional aesthetic arguments for the color arc:

p +
  scale_color_viridis_c(
    option = "inferno",
    breaks = scales::breaks_pretty(10),
    guide = guide_colormeter(
      arc_width = 1/6, # thinner arcs
      arc_gap = 1/3, # bigger gaps
      arc_rounding = 0.03 # rounded corners
    )
  )

By default, label and dashboard radii are derived from arc_radius:

p +
  scale_color_viridis_c(
    option = "inferno",
    breaks = scales::breaks_pretty(10),
    guide = guide_colormeter(
      arc_radius = 1.2
    )
  )

You can use arc_range to set the start and end angles of the color meter, which may yield different shapes:

p +
  scale_color_viridis_c(
    option = "inferno",
    breaks = scales::breaks_pretty(5), # half the arcs
    guide = guide_colormeter(
      arc_range = c(-pi/2, 0) # quarter circle
    )
  )

The defaults aren’t great for when you change from the dashboard shape. Some manual adjustments may be desirable:

p +
  scale_color_viridis_c(
    option = "inferno",
    breaks = scales::breaks_pretty(5),
    guide = guide_colormeter(
      arc_range = c(-pi/2, 0),
      title_position = c(-.2, .2), # moves title left and up from center
      legend_padding = grid::unit(0.7, "lines") # pads relative to legend label
    )
  )

3) Label

formals(guide_colormeter)[grepl("label", names(formals(guide_colormeter)))]
#> $label.theme
#> NULL
#> 
#> $label_radius
#> arc_radius * 1.25

By default, the dashboard radius is derived from label_radius:

p +
  scale_color_viridis_c(
    option = "inferno",
    breaks = scales::breaks_pretty(10),
    guide = guide_colormeter(
      label_radius = 1.5
    )
  )

Like ggplot2::guide_colorsteps(), the argument show.limits controls labeling the limits of the scale:

p +
  scale_color_viridis_c(
    option = "inferno",
    breaks = scales::breaks_pretty(10),
    guide = guide_colormeter(
      label_radius = 1.3,
      show.limits = TRUE
    )
  )

4) Dashboard

formals(guide_colormeter)[grepl("dashboard", names(formals(guide_colormeter)))]
#> $dashboard_radius
#> label_radius * 1.2
#> 
#> $dashboard_color
#> [1] "black"
#> 
#> $dashboard_fill
#> [1] NA
#> 
#> $dashboard_linewidth
#> [1] 0.5
#> 
#> $dashboard_linetype
#> [1] 1
#> 
#> $clip_dashboard
#> [1] TRUE
#> 
#> $close_dashboard
#> clip_dashboard

dashboard_radius controls the radius of just the dashboard circle

p +
  scale_color_viridis_c(
    option = "inferno",
    breaks = scales::breaks_pretty(10),
    guide = guide_colormeter(
      dashboard_radius = 1.2,
    )
  )

By default, the dashboard is clipped to the legend boundary, which can be turned off:

p +
  scale_color_viridis_c(
    option = "inferno",
    breaks = scales::breaks_pretty(10),
    guide = guide_colormeter(
      title = "mpg<br><br>
        <span style='color:darkgrey;font-size:12px'>miles per gallon</span>",
      clip_dashboard = FALSE
    )
  ) +
  theme(legend.title = ggtext::element_markdown(vjust = -.6))

Non-positional aesthetic arguments for the dashboard:

p +
  scale_color_viridis_c(
    option = "inferno",
    breaks = scales::breaks_pretty(10),
    guide = guide_colormeter(
      dashboard_fill = "skyblue",
      dashboard_color = "steelblue",
      dashboard_linetype = 5,
      dashboard_linewidth = 4
    )
  )

5) Frame

formals(guide_colormeter)[grepl("frame", names(formals(guide_colormeter)))]
#> $frame_color
#> [1] NA
#> 
#> $frame_linewidth
#> [1] 0.5
#> 
#> $frame_linetype
#> [1] 1

Frames simply decorate the color arcs/bars:

p +
  scale_color_viridis_c(
    option = "inferno",
    breaks = scales::breaks_pretty(10),
    guide = guide_colormeter(
      frame_color = "black",
      frame_linewidth = .3
    )
  )

Miscellaneous

Set debug = TRUE to inspect the internal legend coordinate system (for deciding on dashboard_radius, arc_width, title_position, etc.):

p +
  scale_color_viridis_c(
    option = "inferno",
    breaks = scales::breaks_pretty(10),
    guide = guide_colormeter(debug = TRUE)
  )

Puttings labels inside the arc:

p +
  scale_color_viridis_c(
    option = "inferno",
    breaks = scales::breaks_pretty(5),
    guide = guide_colormeter(
      arc_width = 0.1,
      label_radius = .7,
      aspect.ratio = 1.1,
      dashboard_color = NA
    )
  ) +
  theme(legend.position = c(.85, .75))

Acknowledgments

Thomas Lin Pedersen for {ggforce}, whose several unexported functions are used in this package.