子图内及子图间行数不均的tableGrob对对齐问题

要实现所有表格子图的顶部对齐，核心是修改布局函数的垂直对齐参数，强制所有表格在各自的容器内顶部定位。以下是两种可行的修正方案：

方案1：修改gridExtra::arrangeGrob的对齐参数 #

原代码中arrangeGrob默认采用垂直居中对齐，导致不同行数的表格无法顶部对齐。只需在每次调用arrangeGrob时添加valign = "top"参数即可：

## 修正后的完整代码
library(ggplot2)
library(gridExtra)
library(cowplot)
library(ggpubr)

# 数据准备
dataA <- data.frame("A" = rep("A", 3),"B" = rep("B", 3),"C" = rep("C", 3))
dataB <- data.frame("A" = rep("A", 4),"B" = rep("B", 4),"C" = rep("C", 4))
dataC <- data.frame("A" = rep("A", 5),"B" = rep("B", 5),"C" = rep("C", 5))
dataD <- data.frame("A" = rep("A", 3),"B" = rep("B", 3),"C" = rep("C", 3))

# 转换为Grob并设置顶部对齐
fig_subplotA <- arrangeGrob(
  tableGrob(dataA, rows = NULL),
  tableGrob(dataB, rows = NULL), 
  ncol = 2,
  valign = "top"  # 子图内表格顶部对齐
)

fig_subplotB <- arrangeGrob(
  tableGrob(dataC, rows = NULL), 
  tableGrob(dataD, rows = NULL), 
  ncol = 2,
  valign = "top"  # 子图内表格顶部对齐
)

# 最终组合图，设置整体顶部对齐
g <- list(fig_subplotA, fig_subplotB)
p.final <- arrangeGrob(grobs = g, ncol = 2, valign = "top")

p <- as_ggplot(p.final) +
  draw_plot_label(label = c("a", "b"), x = c(0, 0.5))

p

# 导出
ggsave(filename = "FigureExample.png", p, width = 4, height = 3)

方案2：使用cowplot::plot_grid更直观控制对齐 #

cowplot的plot_grid函数对齐参数更灵活，通过align和axis参数可精准控制顶部对齐：

## 使用cowplot的实现代码
library(ggplot2)
library(gridExtra)
library(cowplot)
library(ggpubr)

# 数据准备
dataA <- data.frame("A" = rep("A", 3),"B" = rep("B", 3),"C" = rep("C", 3))
dataB <- data.frame("A" = rep("A", 4),"B" = rep("B", 4),"C" = rep("C", 4))
dataC <- data.frame("A" = rep("A", 5),"B" = rep("B", 5),"C" = rep("C", 5))
dataD <- data.frame("A" = rep("A", 3),"B" = rep("B", 3),"C" = rep("C", 3))

# 生成单个表格Grob
tabA <- tableGrob(dataA, rows = NULL)
tabB <- tableGrob(dataB, rows = NULL)
tabC <- tableGrob(dataC, rows = NULL)
tabD <- tableGrob(dataD, rows = NULL)

# 组合每行的两个表格，水平对齐且顶部对齐
row1 <- plot_grid(tabA, tabB, ncol = 2, align = "h", axis = "t")
row2 <- plot_grid(tabC, tabD, ncol = 2, align = "h", axis = "t")

# 组合两行，垂直对齐且顶部对齐
p.final <- plot_grid(row1, row2, ncol = 2, align = "v", axis = "t")

# 添加标签
p <- as_ggplot(p.final) +
  draw_plot_label(label = c("a", "b"), x = c(0, 0.5))

p

# 导出
ggsave(filename = "FigureExample.png", p, width = 4, height = 3)

补充优化：移除表格默认顶部空白 #

如果表格顶部仍有多余空白，可以自定义tableGrob的主题，减少顶部padding：

# 自定义表格主题，移除顶部额外空白
table_theme <- ttheme_default(
  padding = unit(c(0, 0, 0, 0), "mm"),  # 容器上下左右padding设为0
  core = list(padding = unit(c(2, 2), "mm"))  # 保留单元格内的上下padding
)

# 使用自定义主题创建表格Grob
tabA <- tableGrob(dataA, rows = NULL, theme = table_theme)

内容的提问来源于stack exchange，提问作者bgfritz1