legend_keys: Customize Legend Key Appearance

Description

Modify the appearance of legend keys (the symbols/glyphs in the legend) without affecting the plot itself. This is a simpler alternative to using guide_legend(override.aes = list(...)).

Usage

legend_keys(
  size = NULL,
  alpha = NULL,
  shape = NULL,
  linewidth = NULL,
  linetype = NULL,
  fill = NULL,
  colour = NULL,
  color = NULL,
  stroke = NULL,
  aesthetic = c("colour", "fill")
)

Value

A list of ggplot2 guide specifications.

Arguments

size

Numeric. Size of point keys.

alpha

Numeric. Alpha (transparency) of keys, between 0 and 1.

shape

Shape of point keys. Can be:

Numeric (0-25): Standard ggplot2 shape codes
Character name: "circle", "square", "diamond", "triangle", "triangle_down", "plus", "cross", "asterisk", "circle_open", "square_open", "diamond_open", "triangle_open", "circle_filled", "square_filled", "diamond_filled", "triangle_filled"

Shapes 21-25 (or names ending in "_filled") support both outline (colour) and fill (fill) colors.

linewidth

Numeric. Width of line keys.

linetype

Character or numeric. Line type for line keys.

fill

Character. Fill color for filled shapes (shapes 21-25). For shapes 0-20, use colour instead.

colour, color

Character. Outline/stroke color for keys. For shapes 21-25, this controls the outline; for shapes 0-20, this is the main color.

stroke

Numeric. Stroke width for point outlines (shapes 21-25).

aesthetic

Character vector specifying which aesthetic(s) to modify. Default is c("colour", "fill") which covers most common cases. Use "all" to apply to all legends.

Details

This function wraps guide_legend(override.aes = ...) to provide a cleaner interface for common legend key modifications. It's particularly useful for:

Making small points more visible in the legend
Removing transparency from legend keys
Changing symbol shapes to improve clarity
Adding outlines to filled shapes for better visibility

Shape types:

Shapes 0-14: Outline only (color from colour)
Shapes 15-20: Filled solid (color from colour)
Shapes 21-25: Outline + fill (outline from colour, interior from fill)

Important note for filled shapes (21-25):

When using filled shapes with both outline and fill colors, the behavior depends on which aesthetics are mapped in your original plot:

White fill, colored outline: Works with aes(color = var). Use legend_keys(shape = "circle_filled", fill = "white").
Colored fill, black outline: Requires aes(color = var, fill = var) in your plot. Then use legend_keys(colour = "black").

This is because override.aes can only set static values; it cannot inherit from mapped aesthetics. If you only map color and try to override the outline to black, the fill will not have a color mapping to use.

Only non-NULL arguments are applied, so you can selectively modify specific properties.

Examples

Run this code

library(ggplot2)

# Points get lost in legend - make them bigger
ggplot(mtcars, aes(mpg, wt, color = factor(cyl))) +
  geom_point(size = 1) +
  legend_keys(size = 4)

# Remove transparency from legend
ggplot(mtcars, aes(mpg, wt, color = factor(cyl))) +
  geom_point(alpha = 0.3, size = 3) +
  legend_keys(alpha = 1)

# Change shape using name
ggplot(mtcars, aes(mpg, wt, color = factor(cyl))) +
  geom_point(size = 3) +
  legend_keys(shape = "square")

# Filled shape with white fill and colored outline (shapes 21-25)
# Works because we set fill to a static color (white)
ggplot(mtcars, aes(mpg, wt, color = factor(cyl))) +
  geom_point(size = 3) +
  legend_keys(shape = "circle_filled", fill = "white", stroke = 1.5)

# Colored fill with black outline - MUST map both color AND fill in the plot
# This is a ggplot2 limitation: override.aes can only set static values,
# it cannot make fill "inherit" from color
ggplot(mtcars, aes(mpg, wt, color = factor(cyl), fill = factor(cyl))) +
  geom_point(size = 3, shape = 21, stroke = 1) +
  legend_keys(colour = "black", stroke = 1)

# Apply to fill aesthetic (e.g., for boxplots)
ggplot(mtcars, aes(factor(cyl), mpg, fill = factor(cyl))) +
  geom_boxplot(alpha = 0.5) +
  legend_keys(alpha = 1, aesthetic = "fill")