Multiple Legends

Overview

When a plot maps multiple aesthetics (colour, size, shape, etc.), ggplot2 creates separate legends for each. ggguides provides functions to control these legends individually:

• Hide specific legends with legend_hide()
• Keep only certain legends with legend_select()
• Control display order with legend_order_guides()
• Force merge/split with legend_merge() and legend_split()
• Position legends separately using by parameter on position functions
• Style legends separately using by parameter on legend_style()

Example Plot

# Plot with multiple aesthetics
p <- ggplot(mtcars, aes(mpg, wt,
                        color = factor(cyl),
                        size = hp,
                        shape = factor(am))) +
  geom_point() +
  labs(color = "Cylinders", size = "Horsepower", shape = "Transmission")

p

Hiding Legends

Use legend_hide() to remove specific legends while keeping others:

# Hide the size legend
p + legend_hide(size)

# Hide multiple legends
p + legend_hide(size, shape)

Selecting Legends

Use legend_select() to keep only certain legends (inverse of legend_hide()):

# Keep only the colour legend
p + legend_select(colour)

# Keep colour and shape
p + legend_select(colour, shape)

Controlling Legend Order

By default, legends appear in an unspecified order. Use legend_order_guides() to control the display order:

# Default order
p

# Size legend first, then colour, then shape
p + legend_order_guides(size = 1, colour = 2, shape = 3)

Merging and Splitting Legends

ggplot2 automatically merges legends when they have the same title and matching labels. Use legend_merge() and legend_split() to override this behavior.

# Plot where colour and fill map to the same variable
p_merge <- ggplot(mtcars, aes(mpg, wt, color = factor(cyl), fill = factor(cyl))) +
  geom_point(shape = 21, size = 4, stroke = 1.5) +
  labs(color = "Cylinders", fill = "Cylinders")

# Legends merge automatically when titles and labels match
p_merge

# Explicitly request merge (reinforces default behavior)
p_merge + legend_merge(colour, fill)

# Force separate legends even when they could merge
p_merge + legend_split(colour, fill)

Positioning Legends Separately

Position functions (legend_left(), legend_right(), legend_top(), legend_bottom()) accept a by parameter to position specific legends:

# Place colour legend on the left, size legend at bottom
p +
  legend_hide(shape) +
  legend_left(by = "colour") +
  legend_bottom(by = "size")

# Colour legend on top, size on right
p +
  legend_hide(shape) +
  legend_top(by = "colour") +
  legend_right(by = "size")

Styling Legends Separately

Use the by parameter on legend_style() to apply different styles to different legends:

p +
  legend_hide(shape) +
  legend_style(title_face = "bold", background = "grey95", by = "colour") +
  legend_style(size = 10, by = "size")

Combining Multiple Controls

All functions work together:

# Complex example: hide shape, position colour on left with bold title,
# position size at bottom with smaller text
p +
  legend_hide(shape) +
  legend_left(by = "colour") +
  legend_style(title_face = "bold", title_size = 14, by = "colour") +
  legend_bottom(by = "size") +
  legend_style(size = 9, direction = "horizontal", by = "size")

Summary

Learn more:

• Legend Positioning for single-legend placement
• Styling & Customization for legend appearance
• Patchwork Integration for multi-panel plots