Multiple Legends

Gilles Colling

2026-04-22

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:

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.

Forcing Merge

# 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)

Forcing Split

# 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")

Four Legends, One per Side

When a plot has four legends and you want one on each side (top, bottom, left, right), you can fine-tune each legend along three axes:

  1. Side placement — legend_top/bottom/left/right(by = "<aes>")

  2. Distance from the panel — legend_style(by = "<aes>", margin = c(t, r, b, l))

  3. Slide along the side — legend_style(by = "<aes>", justification = ...)

For top/bottom legends, justification is "left", "center", "right" (or a number in [0, 1]). For left/right legends, it’s "top", "center", "bottom" (or a number).

p4 <- ggplot(mtcars, aes(mpg, wt,
                         colour = factor(cyl),
                         fill   = factor(gear),
                         size   = hp,
                         shape  = factor(am))) +
  geom_point(stroke = 1.2) +
  labs(colour = "Cyl", fill = "Gear", size = "HP", shape = "AM")

p4 +
  # 1. Send each legend to its side
  legend_top   (by = "colour") +
  legend_bottom(by = "fill")   +
  legend_left  (by = "size")   +
  legend_right (by = "shape")  +

  # 2. Slide each legend along its side
  legend_style(by = "colour", justification = "left") +
  legend_style(by = "fill",   justification = "right") +
  legend_style(by = "size",   justification = "top") +
  legend_style(by = "shape",  justification = "bottom") +

  # 3. Nudge each legend toward/away from the panel via margin (cm)
  legend_style(by = "colour", margin = c(0, 0, 0.3, 0)) +
  legend_style(by = "fill",   margin = c(0.3, 0, 0, 0)) +
  legend_style(by = "size",   margin = c(0, 0.3, 0, 0)) +
  legend_style(by = "shape",  margin = c(0, 0, 0, 0.3))

Each legend_style(by = ...) call is additive — you can chain as many as you need to tune one legend at a time without affecting the others.

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

Function Purpose Parameters
legend_hide() Hide specific legends Aesthetic names (unquoted)
legend_select() Keep only specific legends Aesthetic names (unquoted)
legend_order_guides() Control legend display order Named args: aes = order
legend_merge() Force legends to merge Aesthetic names (unquoted)
legend_split() Force legends to stay separate Aesthetic names (unquoted)
legend_left(by=) Position one legend on left by = "aesthetic"
legend_style(by=) Style one legend by = "aesthetic" + style args

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