如何消除ggplot中各柱状图颜色间的空白？

Hey there! I totally get how frustrating those tiny gaps between dodged bar segments can be—they mess up the clean, polished look you’re going for. Let’s walk through the most common fix for this issue, since I’ve dealt with this exact problem plenty of times before.

The Core Problem & Solution #

When you create grouped (dodged) bar charts in ggplot, those gaps usually pop up because the width of the bars themselves doesn’t align with the width used to position the dodged groups. Here’s how to make them sit flush:

1. Set matching width values for both geom_col() (or geom_bar()) and position_dodge().

For example, if your original code looks something like this:

ggplot(your_data, aes(x = your_x_var, y = your_y_var, fill = your_group_var)) +
  geom_col(position = "dodge")

Update it to explicitly define matching widths (you can tweak the 0.8 value to fit your plot’s style):

ggplot(your_data, aes(x = your_x_var, y = your_y_var, fill = your_group_var)) +
  geom_col(width = 0.8, position = position_dodge(width = 0.8))

Why This Works #

By default, geom_col() uses a width of 0.9, and position_dodge() also defaults to 0.9—but subtle inconsistencies (like from data structure or other plot customizations) can create tiny gaps. Setting both to the same value forces the grouped bars to lock together perfectly, eliminating those annoying spaces.

Extra Checks If It Still Doesn’t Work #

• Make sure you don’t have any unexpected NA values in your data that might be throwing off the bar positioning.
• If you’re using scale_x_discrete(), double-check that you haven’t added extra padding with the expand parameter (this affects space around the entire plot, not segment gaps, but it’s worth ruling out).

内容的提问来源于stack exchange，提问作者ak3191