r - 将标题添加到 ggplot2 图中，因为标题显示在 facet_wrap 图中

Question

可以为单个情节添加标题，例如:

library(ggplot2)
gdURL <- "http://www.stat.ubc.ca/~jenny/notOcto/STAT545A/examples/gapminder/data/gapminderDataFiveYear.txt"
gDat <- read.delim(file = gdURL)
jDat <- droplevels(subset(gDat, continent != "Oceania"))
str(jDat)

jYear <- 2007
q <- ggplot(subset(jDat, year == jYear),
            aes(x = gdpPercap, y = lifeExp)) + scale_x_log10()
q + geom_point()

q + geom_point(aes(size = sqrt(pop/pi)), pch = 21)

正如标题在这样的 facet_wrap 图中显示(在一个灰色框中并与图集成)？？:

r <- q +
   geom_point(aes(size = sqrt(pop/pi)), pch = 21, show_guide = FALSE) +
   scale_size_continuous(range=c(1,40))

r <- r + facet_wrap(~ continent)
r + aes(fill = continent)

Answer 1

根据@jraab 评论，实现此目的的一种方法是添加一个虚拟列并使用 facet_grid :

jDat$dummy <- NA

ggplot(subset(jDat, year == jYear), aes(x = gdpPercap, y = lifeExp)) +
  scale_x_log10() +
  geom_point() +
  facet_grid(. ~ dummy)

如果你想操纵标题，你可以使用:
facet_grid(. ~ dummy, labeller=label_bquote("My New Title"))