Add a common Legend for combined ggplots

Adding a Common Legend for Combined ggplots 😎📊

Are you struggling to add a common legend to your combined ggplots? Don't worry, we've got you covered! 🙌 In this blog post, we'll address this common issue and provide you with easy solutions to make your plots look even more professional. Let's dive in! 💪

The Problem 😕

One of our readers was having trouble extracting the legend from individual ggplots and adding it to the combined plot. They were aligning the plots horizontally using the grid.arrange function but couldn't find an updated solution to add the common legend.

The Data 📉

Before we jump into the solutions, let's take a quick look at the data provided by our reader:

# Data plot 1
        axis1     axis2   
group1 -0.212201  0.358867
group2 -0.279756 -0.126194
group3  0.186860 -0.203273
group4  0.417117 -0.002592
group1 -0.212201  0.358867
group2 -0.279756 -0.126194
group3  0.186860 -0.203273
group4  0.186860 -0.203273

# Data plot 2   
        axis1     axis2
group1  0.211826 -0.306214
group2 -0.072626  0.104988
group3 -0.072626  0.104988
group4 -0.072626  0.104988
group1  0.211826 -0.306214
group2 -0.072626  0.104988
group3 -0.072626  0.104988
group4 -0.072626  0.104988

The Solutions 🛠️

Solution 1: Using cowplot 🐄

One option to solve this problem is by using the cowplot package, which provides convenient functions for aligning and arranging plots. Here's how you can do it:

1. Install the cowplot package if you haven't already:

install.packages("cowplot")

1. Load the required libraries:

library(ggplot2)
library(cowplot)

1. Create your individual ggplot objects (p1 and p2):

p1 <- ggplot(data1, aes(x = x1, y = y1, colour = groups)) +
  geom_point(position = position_jitter(w = 0.04, h = 0.02), size = 1.8)

p2 <- ggplot(data2, aes(x = x2, y = y2, colour = groups)) +
  geom_point(position = position_jitter(w = 0.04, h = 0.02), size = 1.8)

1. Add a common legend using the get_legend() function from the cowplot package:

combined_plot <- plot_grid(p1 + theme(legend.position = "none"),
                           p2 + theme(legend.position = "none"),
                           get_legend(p1, p2),
                           nrow = 1,
                           widths = unit(c(10, 10), "cm"),
                           heights = unit(rep(8, 1), "cm"))

1. Display the combined plot:

print(combined_plot)

Solution 2: Using patchwork 🧩

Another option is to use the patchwork package, which allows you to easily combine multiple ggplots. Here's how:

1. Install the patchwork package if needed:

install.packages("patchwork")

1. Load the required libraries:

library(ggplot2)
library(patchwork)

1. Create your individual ggplot objects (p1 and p2):

p1 <- ggplot(data1, aes(x = x1, y = y1, colour = groups)) +
  geom_point(position = position_jitter(w = 0.04, h = 0.02), size = 1.8)

p2 <- ggplot(data2, aes(x = x2, y = y2, colour = groups)) +
  geom_point(position = position_jitter(w = 0.04, h = 0.02), size = 1.8)

1. Add a common legend using the & operator from the patchwork package:

combined_plot <- p1 + theme(legend.position = "none") +
  p2 + theme(legend.position = "none") +
  plot_layout(ncol = 2, guides = "collect")

1. Display the combined plot:

print(combined_plot)

Isn't it amazing how these packages make it so much easier to create combined ggplots with a common legend? 😍

The Call-to-Action 📣

Now that you've learned how to add a common legend to your combined ggplots, why not give it a try? Experiment with different datasets, plot types, and customizations! And don't forget to share your stunning combined plots with us. We'd love to see what you come up with! 😄

Feel free to leave a comment below if you have any questions or need further assistance. Happy plotting! 🎉📊