How To Join Multiple ggplot2 Plots with cowplot?

Last Updated : 17 Oct, 2021

In this article, we are going to see how to join multiple ggplot2 plots with cowplot. To join multiple ggplot2 plots, we use the plot_grid() function of the cowplot package of R Language.

Syntax: plot_grid(plot1,plot2,label=<label-vector>, ncol, nrow)

Parameters:

plot1 and plot2 are plots that need to be joined.
<label-vector> is a vector that has a collection of labels for plots.
ncol is the number of columns canvas will be divided in.
nrow is the number of rows canvas will be divided in.

Example 1: Two basic ggplot2 plots combined using plot_grid() function.

# Create sample data
set.seed(5642)                             
sample_data1 <- data.frame(
  name = c("Geek1","Geek2","Geek3",
           "Geek4","Geeek5") ,
  value=c(31,12,15,28,45))

sample_data2 <- data.frame(x = rnorm(400))

# Load ggplot2 and cowplot
library("ggplot2") 
library("cowplot")

# Create both plot and store in variable
plot1<-ggplot(sample_data1,
              aes(x = name, y = value)) +
geom_point(size=4)

plot2<-ggplot(sample_data2, aes(x = x)) +
geom_density(alpha=0.8)
plot_grid(plot1, plot2, labels = c('Plot1', 'Plot2'))

Output:

Example 2: Create a gap between plots using NULL as plot value.

To fix the number of columns we use ncol attribute of plot_grid() function.

# Create sample data
set.seed(5642)                             
sample_data <- data.frame(
  name = c("Geek1","Geek2","Geek3",
           "Geek4","Geeek5") ,
  value = c(31,12,15,28,45))

# Load ggplot2 and cowplot
library("ggplot2") 
library("cowplot")

# Create both plot and store in variable
plot1<-ggplot(sample_data, aes(x=name, y=value)) +
geom_bar(stat = "identity")

plot2<-ggplot(sample_data, aes(x = name, y=value)) +
geom_segment( aes(x=name, xend=name, y=0, yend=value)) 

plot_grid(plot1,NULL, NULL, plot2, labels = c(
  'Plot1','','', 'Plot2'), ncol=2)

Output:

Example 3: Side by Side plot with the shared legend.

To create a plot with a shared legend, we create plots without a legend and create a separate legend and combine them.

# Create sample data
set.seed(5642)                             
sample_data <- data.frame(name=c("Geek1","Geek2","Geek3",
                                 "Geek4","Geeek5") ,
                          value=c(31,12,15,28,45))

# Load ggplot2 and cowplot
library("ggplot2") 
library("cowplot")

# Create both plot and store in variable without legend
plot1<-ggplot(sample_data, aes(x=name, y=value, fill=name)) +
geom_bar(stat = "identity") +
theme(legend.position = "none")

plot2<-ggplot(sample_data, aes(x = name, y=value, fill=name)) +  
geom_point(aes(colour = factor(name)), size = 6)+
theme(legend.position = "none")

# combine both plot using plot_grid()
combined_plot<-plot_grid(plot1, plot2,ncol=2)

# extract legend from plot2
legend <- get_legend(
  plot1 +
    guides(color = guide_legend(nrow = 1)) +
    theme(legend.position = "bottom")
)

# Combine combined plot and legend using plot_grid()
plot_grid(combined_plot, legend,ncol=1,rel_heights = c(1, .1))

Output:

Example 4: Side by Side plot with a shared title

To create a plot with a shared title, we create plots without titles and create a separate title and combine them.

# Create sample data
set.seed(5642)                             
sample_data <- data.frame(name=c("Geek1","Geek2",
                                 "Geek3","Geek4","Geeek5") ,
                          value=c(31,12,15,28,45))

# Load ggplot2 and cowplot
library("ggplot2") 
library("cowplot")

# Create both plot and store in variable without legend
plot1<-ggplot(sample_data, aes(x=name, y=value, fill=name)) +
geom_bar(stat = "identity") +
theme(legend.position = "none")

plot2<-ggplot(sample_data, aes(x = name, y=value, fill=name)) +  
geom_point(aes(colour = factor(name)), size = 6)+
theme(legend.position = "none")

# combine both plot using plot_grid()
combined_plot<-plot_grid(plot1, plot2,ncol=2)

# create title for plot
title <- ggdraw() + 
  draw_label(
    "Two Plots together with shared title",
    fontface = 'bold',
    x = 0,
    hjust = 0,
    size = 24,
  )
# Combine combined plot and title using plot_grid()
plot_grid(title, combined_plot ,ncol=1,rel_heights = c(0.1, 1))