分面的ggplot，中间有y轴

Question

假设我有两个并排的图，具有相同的y轴，由以下R代码生成：

df <- data.frame(x=c(5,2,7,3), y=c(11,3,5,6), facet=c(1,1,2,2))
ggplot(df, aes(x, y)) + facet_grid(~facet) + geom_point()

是否可以在两个图之间的中间写y轴文本（例如，10.0,7.5,5.0）？ （优先文本应居中。）

Answer 1

这是一种方式（差不多）使用Baptiste的回复来自这篇SO Display y-axis for each subplot when faceting。不是中间但是很接近

library(ggplot2)
library(gtable)

# your data
df <- data.frame(x=c(5,2,7,3), y=c(11,3,5,6), facet=c(1,1,2,2))

# First plot (a bit of extra space between facets)
p <- ggplot(df, aes(x, y)) + facet_grid(~facet) + 
        geom_point() + 
        theme(panel.margin = unit(1, "lines"),
              axis.text.y  = element_text( hjust=0))

# get y-axis labels 
g <- ggplotGrob(p)
axis <- gtable_filter(g, "axis-l")[["grobs"]][[1]][["children"]][["axis"]][,1]

# remove axis
g[["grobs"]][[4]][["children"]][["axis"]] <- NULL

# build plot & add axis to LHS of left facet
panels <- subset(g$layout, name == "panel")
g <- gtable_add_grob(g, grobs=axis, t = unique(panels$t), l=tail(panels$l, -1)-1)

grid.newpage()
grid.draw(g)