ggplot，跨多个面绘制多行 [英] ggplot, drawing multiple lines across facets

问题描述

我使用ggplot2方法在列中绘制了两个面板，并且希望在x = 4和8处在面板中添加两条垂直线。以下是代码：

  library（ggplot2）
 library（gtable）
 library（grid）
 
 dat < -  data.frame（x = rep（1：10,2），y = 1：20 + rnorm（20），z = c（rep（A，10），rep（B，10）））
 $ b $ （P）; Pg  
 for（i in c（4,8））{
 Pg < -  gtable_add_grob（Pg，moveToGrob（i / 10,0），t = 8， l = 4）
 Pg < -  gtable_add_grob（Pg，lineToGrob（i / 10,1），t = 6，l = 4）
} 
 
 Pg $ layout $ clip < - off
 grid.newpage（）
 grid.draw（Pg）
  

以上代码修改自：

I drew two panels in a column using ggplot2 facet, and would like to add two vertical lines across the panels at x = 4 and 8. The following is the code:

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

dat <- data.frame(x=rep(1:10,2),y=1:20+rnorm(20),z=c(rep("A",10),rep("B",10)))

P <- ggplot(dat,aes(x,y)) + geom_point() + facet_grid(z~.) + xlim(0,10)
Pb <- ggplot_build(P);Pg <- ggplot_gtable(Pb)

for (i in c(4,8)){
    Pg <- gtable_add_grob(Pg, moveToGrob(i/10,0),t=8,l=4)
    Pg <- gtable_add_grob(Pg, lineToGrob(i/10,1),t=6,l=4)
}

Pg$layout$clip <- "off"
grid.newpage()
grid.draw(Pg)

The above code is modified from:ggplot, drawing line between points across facets. And .

There are two problems in this figure. First, only one vertical line was shown. It seems that moveToGrob only worked once.. Second, the shown line is not exact at x = 4. I didn't find the Pb$panel$ranges variable, so is there a way that I can correct the range as well? Thanks a lot.

解决方案

In the simple scenario where panels have common axes and the lines extend across the full y range you can draw lines over the whole gtable cells, having found the correct npc coordinates conversion (cf previous post, updated because ggplot2 keeps changing),

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

dat <- data.frame(x=rep(1:10,2),y=1:20+rnorm(20),z=c(rep("A",10),rep("B",10)))

p <- ggplot(dat,aes(x,y)) + geom_point() + facet_grid(z~.) + xlim(0,10)
pb <- ggplot_build(p)
pg <- ggplot_gtable(pb)


data2npc <- function(x, panel = 1L, axis = "x") {
  range <- pb$layout$panel_ranges[[panel]][[paste0(axis,".range")]]
  scales::rescale(c(range, x), c(0,1))[-c(1,2)]
}


start <- sapply(c(4,8), data2npc, panel=1, axis="x")

pg <- gtable_add_grob(pg, segmentsGrob(x0=start, x1=start, y0=0, y1=1, gp=gpar(lty=2)), t=8, b=6, l=4)

grid.newpage()
grid.draw(pg)

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