R Notebook中ggarrange共用图例出现多余空白绘图的解决问询

Hey there! I’ve run into this exact annoying problem with ggarrange in R Notebooks before—that random blank plot popping up when you enable a shared legend is such a buzzkill. Let’s break down why this happens and fix it for good.

What’s Causing the Blank Plot? #

When you set common.legend = TRUE, ggarrange extracts the legend from your plots and tries to embed it into the layout. In R Notebook’s HTML rendering environment, this sometimes leaves behind a hidden temporary plot that ends up showing as blank. Plus, without a shared legend, the inconsistent plot sizes happen because one plot has extra space allocated for its legend while the other doesn’t.

Solution 1: Manually Extract and Add the Shared Legend #

This method avoids the common.legend parameter entirely by building the layout yourself, which eliminates the blank plot and ensures uniform plot sizes. Here’s how to adjust your code:

# Load required packages (if not already loaded)
library(ggpubr)
library(gridExtra)

# Create your first histogram WITHOUT a legend
p1 <- gghistogram(data, 
                  title="MOTIVATION SCORES", 
                  x="MOTIVATION", 
                  y="..density..", 
                  add_density=TRUE, 
                  add = "median", 
                  rug = TRUE, 
                  bins=15, 
                  color="#69c8ECFF", 
                  fill="#69c8ECFF",
                  legend = "none")  # Disable legend here

# Create your second histogram (keep the legend temporarily)
p2 <- gghistogram(data, 
                  title="MOTIVATION BY AGE GROUP", 
                  x = "MOTIVATION", 
                  y="..density..", 
                  add_density=TRUE, 
                  add = "median", 
                  rug = TRUE, 
                  bins=15, 
                  color = "AGE_GROUP", 
                  fill = "AGE_GROUP", 
                  palette = c("#69c8ECFF", "#E762D7FF"))

# Extract the shared legend from p2
shared_legend <- get_legend(p2)

# Arrange the two plots (remove p2's legend now)
plot_grid <- ggarrange(p1, p2 + theme(legend.position = "none"),
                       ncol = 2,  # Force side-by-side layout
                       align = "h")  # Align plots horizontally for uniform size

# Add the shared legend to the bottom of the plot grid
annotate_figure(plot_grid,
                bottom = shared_legend)

Solution 2: Use grid.arrange for More Control #

If you prefer using gridExtra instead of ggpubr’s annotation tools, this works just as well:

library(gridExtra)

# Reuse p1, p2, and shared_legend from Solution 1

grid.arrange(p1, p2 + theme(legend.position = "none"),
             ncol = 2,
             bottom = shared_legend)

Why This Works #

By manually extracting the legend and adding it after arranging the plots, we avoid the hidden temporary plot that common.legend = TRUE creates in R Notebooks. We also ensure both main plots have identical dimensions (since neither has a legend taking up space), then add the shared legend below them cleanly.

内容的提问来源于stack exchange，提问作者BKV