R and ggplot: Putting x-axis labels outside the panel in ggplot

问题

Is there a way to bring the labels forward with respect to plot panel in ggplot? Actually I was trying to answer my question here. I have not got any satisfactory response to that one although I thought it would be possible in ggplot. This is an attempt to get a solution although a hacky one. But the labels are rendered below the plot panel here.

Following are my (example) data, attempted solution and the resulting plot.

library(ggplot2)
library(magrittr)    
mydata = data.frame(expand.grid(Tag = c('A','B','C'),Year = 2010:2011,PNo = paste0("X-",1:4)),Value = round(runif(24,1,20)))
mydata$dist = ifelse(mydata$Tag == 'A',0,ifelse(mydata$Tag=='B',2,7))

mydata %>% ggplot(aes(x = dist,y = Value,fill = factor(Year))) +geom_bar(stat='summary',position = 'dodge',fun.y='mean',width = 1) +
  facet_wrap(~PNo,ncol=2) +
  theme(axis.text.x = element_blank(),axis.ticks.x = element_blank()) +
  geom_label(data  = mydata %>% filter(PNo %in% c('X-3','X-4')),aes(x = dist,y=0,label = Tag),size=6,inherit.aes=F,color = 'red')

回答1:

You have to turn off clipping of the bottom panel elements:

p <- mydata %>% ggplot(aes(x = dist,y = Value,fill = factor(Year))) +geom_bar(stat='summary',position = 'dodge',fun.y='mean',width = 1) +
  facet_wrap(~PNo,ncol=2) +
  theme(axis.text.x = element_blank(),axis.ticks.x = element_blank()) +
  geom_label(data  = mydata %>% dplyr::filter(PNo %in% c('X-3','X-4')),aes(x = dist,y=0,label = Tag),size=6,inherit.aes=F,color = 'red') 
library(grid) 
gt <- ggplot_gtable(ggplot_build(p)) 
gt$layout$clip[grep("panel-2-\\d+", gt$layout$name)] <- "off"
grid.draw(gt) 

See Point clipped on x-axis in ggplot

来源：https://stackoverflow.com/questions/42633156/r-and-ggplot-putting-x-axis-labels-outside-the-panel-in-ggplot