Create Custom Legend With ggplot in R

  1. Use the legend.position Parameter in the theme Function to Specify Legend Position in R
  2. Use legend.justification and legend.background Parameters in theme Function to Create Custom Legend
  3. Use legend.title Parameter in theme Function to Modify Legend Title Formatting

This article will demonstrate multiple methods to create a custom legend with ggplot in R.

Use the legend.position Parameter in the theme Function to Specify Legend Position in R

The legend.position parameter specifies the legend position in the plot. Optional values can be "none", "left", "right", "bottom", "top" or two-element numeric vector. The plot.title parameter is also utilized in the following example to modify the title of the plot. Finally, two plots are drawn at the same time using the grid.arrange function.

library(ggplot2)
library(gridExtra)
library(babynames)
library(dplyr)

dat <- babynames %>%
  filter(name %in% c("Alice", "Maude", "Mae")) %>%
  filter(sex=="F")

p1 <- ggplot(dat, aes(x = year, y = n, color = name)) +
  geom_line() +
  scale_y_continuous(
    breaks = seq(0, 15000, 1000),
    name = "Number of babies") +
  ggtitle("Name Popularity Through Years")

p2 <- ggplot(dat, aes(x = year, y = n, color = name)) +
  geom_line() +
  scale_y_continuous(
    breaks = seq(0, 15000, 1000),
    name = "Number of babies") +
  theme(
    legend.position = "left",
    plot.title = element_text(
      size = rel(1.2), lineheight = .9,
      family = "Calibri", face = "bold", colour = "brown"
    )) +
  ggtitle("Name Popularity Through Years")

grid.arrange(p1, p2, nrow = 2)

ggplot custom legend 1

Use legend.justification and legend.background Parameters in theme Function to Create Custom Legend

Another useful parameter of the theme function is legend.background which can be used to format the legend background. The following code snippet fills the legend rectangle with white color and a black stroke. Also, legend.justification is combined with legend.position to specify the legend’s position.

library(ggplot2)
library(gridExtra)
library(babynames)
library(dplyr)

dat <- babynames %>%
  filter(name %in% c("Alice", "Maude", "Mae")) %>%
  filter(sex=="F")

p3 <- ggplot(dat, aes(x = year, y = n, color = name)) +
  geom_line() +
  scale_y_continuous(
    breaks = seq(0, 15000, 1000),
    name = "Number of babies") +
  theme(
    legend.position = c(1, 1),
    legend.justification = c(1, 1),
    legend.background = element_rect(fill = "white", colour = "black"),
    plot.title = element_text(
      size = rel(1.2), lineheight = .9,
      family = "Calibri", face = "bold", colour = "brown"
    )) +
  ggtitle("Name Popularity Through Years")


p4 <- ggplot(dat, aes(x = year, y = n, color = name)) +
  geom_line() +
  scale_color_discrete(limits = c("Maude", "Mae", "Alice")) +
  scale_y_continuous(
    breaks = seq(0, 15000, 1000),
    name = "Number of babies") +
  theme(
    legend.position = c(1, 1),
    legend.justification = c(1, 1),
    legend.background = element_rect(fill = "white", colour = "black"),
    plot.title = element_text(
      size = rel(1.2), lineheight = .9,
      family = "Calibri", face = "bold", colour = "brown"
    )) +
  ggtitle("Name Popularity Through Years")

grid.arrange(p3, p4, nrow = 2)

ggplot custom legend 2

Use legend.title Parameter in theme Function to Modify Legend Title Formatting

The legend.title parameter can be utilized to change the legend title formatting. It takes the element_text function with different arguments to modify the formatting like font family, the color of text, or font size. The grid.arrange function is used to demonstrate the change between the two drawn graphs.

library(ggplot2)
library(gridExtra)
library(babynames)
library(dplyr)

dat <- babynames %>%
  filter(name %in% c("Alice", "Maude", "Mae")) %>%
  filter(sex=="F")

p5 <- ggplot(dat, aes(x = year, y = n, color = name)) +
  geom_line() +
  scale_color_discrete(limits = c("Maude", "Mae", "Alice")) +
  labs(color = "Name") +
  scale_y_continuous(
    breaks = seq(0, 15000, 1000),
    name = "Number of babies") +
  theme(
    legend.position = c(1, 1),
    legend.justification = c(1, 1),
    legend.background = element_rect(fill = "white", colour = "black"),
    plot.title = element_text(
      size = rel(1.2), lineheight = .9,
      family = "Calibri", face = "bold", colour = "brown"
    )) +
  ggtitle("Name Popularity Through Years")


p6 <- ggplot(dat, aes(x = year, y = n, color = name)) +
  geom_line() +
  scale_color_discrete(limits = c("Maude", "Mae", "Alice")) +
  labs(color = "Name") +
  scale_y_continuous(
    breaks = seq(0, 15000, 1000),
    name = "Number of babies") +
  theme(
    legend.title = element_text(
      family = "Calibri",
      colour = "brown",
      face = "bold",
      size = 12),
    legend.position = c(1, 1),
    legend.justification = c(1, 1),
    legend.background = element_rect(fill = "white", colour = "black"),
    plot.title = element_text(
      size = rel(1.2), lineheight = .9,
      family = "Calibri", face = "bold", colour = "brown"
    )) +
  ggtitle("Name Popularity Through Years")

grid.arrange(p5, p6, nrow = 2)

ggplot custom legend 3

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