Move ggplot legend into title area

Question

I have a series of paired ggplot charts I am getting to render together using cowplot. However, while the legend is useful, it's getting in the way - the charts that need legends become a lot smaller than their equivalents so you can't compare them as easily. Here's a simple example of the kind of chart I'm creating:

library(dplyr)
library(tidyr)
library(stringr)
library(tibble)
library(ggplot2)
library(cowplot)

df <- mtcars %>%
  rownames_to_column("model") %>%
  filter(str_detect(model, 'Merc')) %>%
  pivot_longer(cols = -model, names_to = 'metric') %>%
  filter(metric %in% c("hp", "drat", "wt"))

p1 <- df %>%
  filter(metric == "hp") %>%
  ggplot(aes(x = metric, y = value)) +
  geom_col() +
  facet_grid(model~.) +
  labs(title = "hp")

p2 <- df %>%
  filter(!metric == "hp") %>%
  ggplot(aes(x = metric, y = value, fill = metric)) +
  geom_col() +
  facet_grid(model~.) +
  labs(title = "drat and wt") +
  theme(legend.position = 'none')

plot_grid(p1, p2)

Which comes out looking like this:

I'd ideally like to drop the legend in the spot I've highlighted in yellow, since there's space, and it visually connects to the chart that needs it. But I have poked my way through assorted documentation for both ggplot2 and cowplot, but I haven't figured it out.

What am I missing?

Answer 1

We can use ggdraw(); just note that this is not exactly a robust solution and you need to tweak the position and size of the legend in the last draw_plot to get it right for your desired aspect ratio.

p1 <- df %>%
  filter(metric == "hp") %>%
  ggplot(aes(x = metric, y = value)) +
  geom_col() +
  facet_grid(model~.) +
  labs(title = "hp")

p2 <- df %>%
  filter(!metric == "hp") %>%
  ggplot(aes(x = metric, y = value, fill = metric)) +
  geom_col() +
  facet_grid(model~.) +
  labs(title = "drat and wt") +
  theme(legend.position = "top",
        legend.direction = "horizontal",
        legend.margin = margin(0, 0, 0, 0),
        legend.box.margin = margin(0, 0, 0, 0))

ggdraw() +
  draw_plot(p1, 
            x = 0, y = 0, width = 0.5, height = 1) +
  draw_plot(p2 + theme(legend.position = 'none'), 
            x = 0.5, y = 0, width = 0.5, height = 1) +
  draw_plot(get_legend(p2), 
            x = 0.72, y = 0.943, width = 0.25, height = 0.07)

^{Created on 2025-07-22 with reprex v2.1.1}

Answer 2

This is an alternative using ggtext, it does not directly answers your question of adding legend next to title, instead we will colour the text to replace the legend:

Add custom colours for fill:

p1 <- df %>%
  filter(metric == "hp") %>%
  ggplot(aes(x = metric, y = value, fill = metric)) +
  geom_col() +
  facet_grid(model~.) +
  scale_fill_manual(
    name = NULL,
    values = c(hp = "#0072B2", drat = "#009E73", wt = "#D55E00"),
    labels = c(
      hp = "<i style='color:#0072B2'>I. hp</i>",
      drat = "<i style='color:#009E73'>I. drat</i>",
      wt = "<i style='color:#D55E00'>I. wt</i>")) +
  theme(legend.position = "none")

p2 <- df %>%
  filter(!metric == "hp") %>%
  ggplot(aes(x = metric, y = value, fill = metric)) +
  geom_col() +
  facet_grid(model~.) +
  scale_fill_manual(
    name = NULL,
    values = c(hp = "#0072B2", drat = "#009E73", wt = "#D55E00"),
    labels = c(
      hp = "<i style='color:#0072B2'>I. hp</i>",
      drat = "<i style='color:#009E73'>I. drat</i>",
      wt = "<i style='color:#D55E00'>I. wt</i>")) +
  theme(legend.position = "none")

I prefer patchwork to combine plots:

library(patchwork)

(p1 | p2) +
  plot_annotation(title = "My title:
  <span style='color:#0072B2;'>hp</span>, 
  <span style='color:#009E73;'>drat</span>, and
  <span style='color:#D55E00;'>wt</span>",
                  theme =  theme(
                    plot.title = element_markdown(lineheight = 1.1),
                    legend.text = element_markdown(size = 11)
                  ))