如何在R语言的条形图中增大不同分组条形之间的间距？

我绘制了一个包含不同生物学过程的水平条形图，这些过程按Group_ID分组着色，且已按Group_ID排序。现在想增大同一Group_ID最后一个条形与下一个Group_ID第一个条形之间的间距。试过geom_bar(position = "dodge")和在每个Group_ID后插入空条形，但都没效果。

我的代码如下：

BP <- data.frame(
  ID=c('Adaptive immune response', 'Immune response', 'Exocytosis', 'Peptide transport', 'Cell-cell adhesion', 'Lipid metabolism'),
  Group_ID=c('Immune Response','Immune Response', 'Secretion And Transport', 'Secretion And Transport',    'Others', 'Others'),
  log10=c(0.8, 0.2, 0.7, 0.9, 0.3, 0.5))

BP$Group_ID <- factor(BP$Group_ID, levels = c("Immune Response", "Secretion And Transport", "Others"))
# 修正代码中的变量名错误：BP_Synu_PD改为BP
BP <- BP[order(BP$Group_ID, decreasing = TRUE),]

ggplot(BP, aes(x = factor(ID, levels = unique(ID)), y = log10, fill = Group_ID)) +
  geom_bar(stat = "identity", position = "identity") +
  coord_flip() +
  scale_y_reverse() +
  labs(title = "Bar Plot of signed log10(FDR)",
       x = "ID",
       y = "Signed log10(FDR)",
       fill = "Group_ID") +
  theme_few() +
  theme(axis.text.y = element_text(size = 12),
        legend.text = element_text(size = 15))

方法1：手动调整x轴位置（无需额外包） #

核心思路是把分类变量ID转换成数值型，给不同组之间的位置添加偏移量，实现组间距增大的效果。

步骤及代码：

library(ggplot2)
library(ggthemes)

# 确保数据按Group_ID排序
BP <- BP[order(BP$Group_ID, decreasing = TRUE),]
# 为每个ID分配初始数值位置
BP$x_pos <- seq_len(nrow(BP))

# 设置组间间距大小（可根据需求调整）
gap_size <- 0.8
# 获取每个组最后一个元素的位置
group_last_pos <- tapply(BP$x_pos, BP$Group_ID, max)

# 为后续组的所有元素添加偏移量
for(i in 2:length(group_last_pos)){
  current_group <- names(group_last_pos)[i]
  BP$x_pos[BP$Group_ID == current_group] <- BP$x_pos[BP$Group_ID == current_group] + (i-1)*gap_size
}

# 绘制图形
ggplot(BP, aes(x = x_pos, y = log10, fill = Group_ID)) +
  geom_bar(stat = "identity", width = 0.8) + # 条形宽度匹配间距
  coord_flip() +
  scale_y_reverse() +
  scale_x_continuous(breaks = BP$x_pos, labels = BP$ID) + # 自定义轴标签
  labs(title = "Bar Plot of signed log10(FDR)",
       x = "ID",
       y = "Signed log10(FDR)",
       fill = "Group_ID") +
  theme_few() +
  theme(axis.text.y = element_text(size = 12),
        legend.text = element_text(size = 15))

方法2：用分面模拟组间距（更简洁） #

利用facet_grid按Group_ID分面，隐藏分面标签和边框，同时调整分面间距，也能实现目标效果：

ggplot(BP, aes(x = factor(ID, levels = unique(ID)), y = log10, fill = Group_ID)) +
  geom_bar(stat = "identity") +
  coord_flip() +
  scale_y_reverse() +
  facet_grid(Group_ID ~ ., scales = "free_y", space = "free_y") + # 自由缩放组内轴空间
  labs(title = "Bar Plot of signed log10(FDR)",
       x = "ID",
       y = "Signed log10(FDR)",
       fill = "Group_ID") +
  theme_few() +
  theme(axis.text.y = element_text(size = 12),
        legend.text = element_text(size = 15),
        strip.background = element_blank(), # 隐藏分面背景
        strip.text.y = element_blank(), # 隐藏分面标签
        panel.spacing.y = unit(1, "cm")) # 自定义组间间距

注：方法2适合组内元素数量差异较大的场景；方法1保持所有条形在同一轴上，视觉统一性更强。

内容的提问来源于stack exchange，提问作者Pia _11