使用gtable替换ggplot2分面面板为自定义图表的问题求助

以下针对你遇到的两个问题提供具体解决方法：

问题1：增加右侧Y轴与图例的间距 #

方式1：调整汇总图的边距 #

直接在生成汇总子图时，通过theme()设置右侧边距，让子图本身留出空白，替换后自然与图例拉开距离：

sub = ggplot(mtcars) +
  aes(x = factor(cyl), fill = factor(am)) +
  geom_bar(position = "fill") +
  scale_fill_discrete(guide = "none") +
  scale_y_continuous(NULL, position = "right", labels = scales::percent) +
  xlab(NULL) +
  theme(plot.margin = margin(t = 0, r = 15, b = 0, l = 0)) # 自定义右侧边距大小

方式2：调整主图gtable的列间距 #

找到图例所在列，在其左侧插入空白列来增加间距：

# 先获取主图gtable
gt = ggplotGrob(p)
# 定位图例所在列
legend_col = gt$layout[gt$layout$name == "guide-box", "l"]
# 在图例左侧添加空白列，宽度可自定义
gt = gtable_add_cols(gt, unit(10, "pt"), pos = legend_col - 1)

问题2：添加缺失的右侧轴空占位符 #

如果原分面图的gtable中没有axis-r-2-2这类组件，需要手动添加空占位grob来保证布局位置正确：

步骤1：确定占位符的位置 #

基于目标panel的布局信息，计算右侧轴应该占据的行和列范围：

panel_name = glue("panel-{row}-{col}")
panel_idx = grep(panel_name, gt$layout$name)
panel_layout_full = gt$layout[panel_idx, ]
# 右侧轴与目标panel同高，位于panel右侧一列
axis_r_pos = list(
  t = panel_layout_full$t,
  l = panel_layout_full$r + 1,
  b = panel_layout_full$b,
  r = panel_layout_full$r + 1
)

步骤2：添加空占位符 #

检查gtable中是否存在目标轴条目，不存在则添加nullGrob()作为占位：

axis_r_name = glue("axis-r-{row}-{col}")
if (length(grep(axis_r_name, gt$layout$name)) == 0) {
  gt = gtable_add_grob(
    gt,
    grobs = nullGrob(),
    name = axis_r_name,
    t = axis_r_pos$t,
    l = axis_r_pos$l,
    b = axis_r_pos$b,
    r = axis_r_pos$r
  )
}
# 之后正常获取轴布局信息并替换
axis_r_idx = grep(axis_r_name, gt$layout$name)
axis_r_layout = as.list(gt$layout[axis_r_idx, c("t", "l", "b", "r")])

整合后的完整代码 #

library(ggplot2)
library(gtable)
library(glue)
library(purrr) # for purrr::partial

get_panel = function(st, x, y) {
  if (missing(x) && missing(y)) {
    name = "panel"
  } else {
    name = glue("panel-{x}-{y}")
  }

  i = st$layout[grep(name, st$layout$name), "t"]
  j = st$layout[grep(name, st$layout$name), "l"]

  st[i, j]
}

get_axis = function(st, pos, x, y) {
  if (missing(x) && missing(y)) {
    name = glue("axis-{pos}")
  } else {
    name = glue("axis-{pos}-{x}-{y}")
  }
  i = st$layout[grep(name, st$layout$name), "t"]
  j = st$layout[grep(name, st$layout$name), "l"]

  if (length(c(i, j)) < 2L) {
    NULL
  } else {
    st[i, j]
  }
}

p = ggplot(mtcars) +
  aes(x = wt, y = mpg, color = factor(am)) +
  geom_point() +
  facet_wrap(~factor(cyl), ncol = 2)

# 调整子图右侧边距解决间距问题
sub = ggplot(mtcars) +
  aes(x = factor(cyl), fill = factor(am)) +
  geom_bar(position = "fill") +
  scale_fill_discrete(guide = "none") +
  scale_y_continuous(NULL, position = "right", labels = scales::percent) +
  xlab(NULL) +
  theme(plot.margin = margin(t = 0, r = 15, b = 0, l = 0))

row = 2
col = 2

gt = ggplotGrob(p)
st = ggplotGrob(sub)

new_panel = get_panel(st)
new_axis_b = get_axis(st, "b")
new_axis_r = get_axis(st, "r")

panel_name = glue("panel-{row}-{col}")
panel_idx = grep(panel_name, gt$layout$name)
panel_layout = as.list(gt$layout[panel_idx, c("t", "l", "b", "r")])

axis_b_name = glue("axis-b-{row}-{col}")
axis_b_idx = grep(axis_b_name, gt$layout$name)
axis_b_layout = as.list(gt$layout[axis_b_idx, c("t", "l", "b", "r")])

# 添加缺失的右侧轴占位符
axis_r_name = glue("axis-r-{row}-{col}")
if (length(grep(axis_r_name, gt$layout$name)) == 0) {
  panel_layout_full = gt$layout[panel_idx, ]
  gt = gtable_add_grob(
    gt,
    grobs = nullGrob(),
    name = axis_r_name,
    t = panel_layout_full$t,
    l = panel_layout_full$r + 1,
    b = panel_layout_full$b,
    r = panel_layout_full$r + 1
  )
}
axis_r_idx = grep(axis_r_name, gt$layout$name)
axis_r_layout = as.list(gt$layout[axis_r_idx, c("t", "l", "b", "r")])

# 替换面板和轴
result = gt |>
  partial(gtable_add_grob, !!!panel_layout)(grobs = new_panel$grob) |>
  partial(gtable_add_grob, !!!axis_b_layout)(grobs = new_axis_b$grob) |>
  partial(gtable_add_grob, !!!axis_r_layout)(grobs = new_axis_r$grob)

plot(result)

内容的提问来源于stack exchange，提问作者mikeck