ggplot2：使用 gtable 将条形标签移动到 facet_grid 面板的顶部

Question

我正在使用facet_grid 创建一个图形，以在 y 轴上刻画一个分类变量。我决定不使用facet_wrap，因为我需要space = 'free' 和labeller = label_parsed。我的标签很长，右侧有一个图例，因此我想将标签从面板右侧移动到面板顶部。

这里有一个例子来说明我在哪里卡住了。

library(ggplot2)
library(gtable)

mt <- ggplot(mpg, aes(x = cty, y = model)) + geom_point() +
  facet_grid(manufacturer ~ ., scales = 'free', space = 'free') +
  theme_minimal() +
  theme(panel.margin = unit(0.5, 'lines'), strip.text.y = element_text(angle = 0))

现在我想将带状文本从每个面板的右侧移动到每个面板的顶部。我可以存储条形标签的 grobs 并将它们从图中删除：

grob <- ggplotGrob(mt)
strips.y <- gtable_filter(grob, 'strip-right')
grob2 <- grob[,-5]

但现在我被 rbind 卡住了 - 将 grobs 退回，所以标签会出现在面板的顶部。

另一种可能的解决方案是使用facet_wrap，然后重新调整面板as discussed in another question 的大小，但在这种情况下，我必须手动更改构面上的标签，因为facet_wrap 没有labeller = label_parsed .

我会很感激任何一种方法的建议！

感谢阅读，

汤姆

Answer 1

这是您的第一种方法。它在每个面板上方插入一行，抓住条形 grobs（在右侧），并将它们插入新行。

library(ggplot2)
library(gtable)
library(grid)

mt <- ggplot(mpg, aes(x = cty, y = model)) + geom_point() +
  facet_grid(manufacturer ~ ., scales = 'free', space = 'free') +
  theme(panel.spacing = unit(0.5, 'lines'), 
         strip.text.y = element_text(angle = 0))

# Get the gtable
gt <- ggplotGrob(mt)

# Get the position of the panels in the layout
panels <-c(subset(gt$layout, grepl("panel", gt$layout$name), se=t:r))

# Add a row above each panel
for(i in rev(panels$t-1)) gt = gtable_add_rows(gt, unit(.5, "lines"), i)

# Get the positions of the panels and the strips in the revised layout
panels <-c(subset(gt$layout, grepl("panel", gt$layout$name), se=t:r))
strips <- c(subset(gt$layout, grepl("strip-r", gt$layout$name), se=t:r))

# Get the strip grobs
stripText = gtable_filter(gt, "strip-r")

# Insert the strip grobs into the new rows
for(i in 1:length(strips$t)) gt = gtable_add_grob(gt, stripText$grobs[[i]]$grobs[[1]],  t=panels$t[i]-1, l=4)

# Remove the old strips
gt = gt[,-5]

# For this plot - adjust the heights of the strips and the empty row above the strips
for(i in panels$t) {
   gt$heights[i-1] = unit(0.8, "lines")
   gt$heights[i-2] = unit(0.2, "lines")
   }

# Draw it
grid.newpage()
grid.draw(gt)

或者，您可以使用facet_wrap_labeller 函数available from here 实现第二种方法。

library(ggplot2)
library(gtable)

mt <- ggplot(mpg, aes(x = cty, y = model)) + geom_point() +
   facet_wrap(~ manufacturer, scales = "free_y", ncol = 1) +
   theme(panel.margin = unit(0.2, 'lines'))


facet_wrap_labeller <- function(gg.plot, labels=NULL) {
  require(gridExtra)

  g <- ggplotGrob(gg.plot)
  gg <- g$grobs      
  strips <- grep("strip_t", names(gg))

  for(ii in seq_along(labels))  {
    modgrob <- getGrob(gg[[strips[ii]]], "strip.text", 
                       grep=TRUE, global=TRUE)
    gg[[strips[ii]]]$children[[modgrob$name]] <- editGrob(modgrob,label=labels[ii])
  }

  g$grobs <- gg
  class(g) = c("arrange", "ggplot",class(g)) 
  return(g)
}

## Number of y breaks in each panel
g <- ggplot_build(mt) 
N <- sapply(lapply(g$panel$ranges, "[[", "y.major"), length)

# Some arbitrary strip texts
StripTexts = expression(gamma[1], sqrt(gamma[2]), C, `A really incredibly very very very long label`, gamma[5], alpha[1], alpha[2], `Land Rover`, alpha[1], beta[2], gamma^2, delta^2, epsilon[2], zeta[3], eta[4] )

 # Apply the facet_wrap_labeller function
gt = facet_wrap_labeller(mt, StripTexts)

# Get the position of the panels in the layout
panels <- gt$layout$t[grepl("panel", gt$layout$name)]

# Replace the default panel heights with relative heights
gt$heights[panels] <- lapply(N, unit, "null")

# Draw it
gt

Answer 2

我正在努力解决类似的问题，但将标签放在底部。我使用了这个答案的代码改编。而最近发现

ggplot2 ver.2.2.1.0 (http://docs.ggplot2.org/current/facet_grid.html)

~facet_grid(.~variable,switch='x')

对我来说效果很好的选项。