ggplot facet_grid设置y轴标签居右后面板间距错位问题求助

I totally feel your pain—getting facet alignment right in ggplot2 when tweaking axis positions can be such a headache. Let's break down what's causing your issue and go through the best solutions to keep your y-axis labels on the right while keeping everything perfectly aligned.

What's Causing the Misalignment? #

Your problem stems from ggplot2's default behavior for discrete axes: when you move the y-axis to the right with scale_y_discrete(position="right"), the default expand parameter adds small padding around the plot area. This padding throws off the alignment between your y-side facet strips (the category labels) and the tile panels because the facet spacing calculations don't account for this extra padding correctly.

Adjusting panel.spacing didn't help because that setting controls the gap between separate panels (like between group 1 and group 2), not the alignment between a facet strip and its corresponding panel.

Best Solutions #

1. Your Current Fix (Clean & Targeted) #

The solution you discovered—adding expand = c(0,0) to scale_y_discrete—is actually one of the best approaches. It removes the default padding from the y-axis, making the edge of the tile panel line up perfectly with the facet strip. Here's the cleaned-up code for reference:

library(data.table)
library(ggplot2)

# Sample data
td = data.table(
  Sym=rep(paste0("sym",1:14),141), 
  sample=rep(paste0("sample",1:141), 14), 
  value = sample(x=0:100, size=141*14,replace=T)/100, 
  group = rep(c(rep(1,12),rep(2,34),rep(3,28),rep(4,27),rep(5,40)),14)
)
td[, category := ifelse(
  Sym %in% paste0("sym",1:5), "cat1", 
  ifelse(Sym %in% paste0("sym",6:10), "cat2", 
         ifelse(Sym %in% paste0("sym",11:14), "cat3",NA))
)]

# Fixed plot
p = ggplot(td, aes(x=sample,y=Sym, fill=value))+
  geom_tile()+
  facet_grid(category ~ group, scales = "free", space = "free", switch = "y")+
  scale_y_discrete(position = "right", expand = c(0, 0))+  # Critical fix
  theme(
    axis.title = element_blank(), 
    axis.ticks = element_blank(), 
    axis.text.x = element_blank(), 
    axis.line = element_blank(), 
    strip.text.y = element_text(angle=180), 
    strip.text.x = element_text(color="white")
  )
p

This works because it eliminates the extra space that was pushing the panel away from the facet strip. It's targeted (only affects the y-axis) and doesn't disrupt other parts of your plot.

2. Alternative: Uniform Expansion Control with coord_cartesian #

If you ever want to remove padding from both axes at once (though you might not need this for your specific plot), you can use coord_cartesian(expand = FALSE) instead. Just note this will affect both x and y axes:

p + coord_cartesian(expand = FALSE)

Since your x-axis already hides text and ticks, this won't cause issues—but the first method is more precise for keeping only the y-axis aligned.

3. Fine-Tuning Panel Gaps (If Needed) #

If you want to add a tiny gap between y-axis facet panels without breaking alignment, combine the expand = c(0,0) fix with a small panel.spacing.y value:

p + 
  scale_y_discrete(position = "right", expand = c(0, 0)) +
  theme(panel.spacing.y = unit(0.1, "lines"))  # Adds subtle gap between y-facet panels

内容的提问来源于stack exchange，提问作者Reilstein