如何在刻面时在图下显示条形标签？

Question

似乎这些条总是在由ggplot2创建的图上方。他们可以移动到情节之下吗？

例如：

library(ggplot2) 
qplot(hwy, cty, data = mpg) + facet_grid(. ~ manufacturer) 

显示在顶部轿厢的信息。它们可以显示在底部吗？

Answer 1

更新：使用ggplot2版本2.1.0，考虑使用switch = 'x'。详情请参阅?facet_grid。

使用gtable功能，很容易移动钢带。 （还是看here花药版本 - 交换x轴和钢带）

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

p <- ggplot(mpg, aes(hwy, cty)) + geom_point() + facet_grid(. ~ manufacturer) + 
    theme(strip.text.x = element_text(angle = 90, vjust = 1), 
      strip.background = element_rect(fill = NA)) 

# Convert the plot to a grob 
gt <- ggplotGrob(p) 

# Get the positions of the panels in the layout: t = top, l = left, ... 
panels <-c(subset(gt$layout, grepl("panel", gt$layout$name), select = t:r)) 

# Add a row below the x-axis tick mark labels, 
# the same height as the strip 
gt = gtable_add_rows(gt, gt$height[min(panels$t)-1], max(panels$b) + 2) 

# Get the strip grob 
stripGrob = gtable_filter(gt, "strip-t") 

# Insert the strip grob into the new row 
gt = gtable_add_grob(gt, stripGrob, t = max(panels$b) + 3, l = min(panels$l), r = max(panels$r)) 

# remove the old strip 
gt = gt[-(min(panels$t)-1), ] 

grid.newpage() 
grid.draw(gt)