ggplot，在各个方面绘制多条线 [英] ggplot, drawing multiple lines across facets

问题描述

我使用ggplot2 facet在一列中绘制了两个面板，并想在x = 4和8处的面板上添加两条垂直线.以下是代码:

库(ggplot2)图书馆(gtable)图书馆(网格)数据 <- 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 <-关闭"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

Updated to ggplot2 V3.0.0

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_params[[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=7, b=9, l=5)

grid.newpage()
grid.draw(pg)

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