r - ggplot2: Using gtable to move strip labels to top of panel for facet_grid

Question

I am creating a graphic using facet_grid to facet a categorical variable on the y-axis. I decided not to use facet_wrap because I need space = 'free' and labeller = label_parsed. My labels are long and I have a legend on the right so I would like to move the labels from the right of the panel to the top of the panel.

Here is an example to show where I'm getting stuck.

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))

Now I would like to move the strip text from the right of each panel to the top of each panel. I can store the grobs for the strip labels and remove them from the plot:

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

But now I'm stuck when it comes to rbind-ing the grobs back so the labels go to the top of the panels.

Another possible solution would be to use facet_wrap and then re-size the panels as discussed in another question, but in that case I would have to manually change the labels on the facets because there is no labeller = label_parsed for facet_wrap.

I'd appreciate suggestions on either approach!

Thanks for reading,

Tom

Answer 1

这需要您的第一种方法。它在每个面板上方插入一行，抓取条形 grobs（在右侧），并将它们插入新行中。

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，您可以使用此处提供facet_wrap_labeller的功能来实现第二种方法。

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。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。