我想绘制一个矩形注释，它将跨越 ggplot 中的构面边界。
library(ggplot2)
myPlot <- ggplot(mpg, aes(displ, hwy)) +
geom_point() +
facet_grid(class ~ .)
# add annotation
myPlot +
annotate("rect", xmin = 3, xmax = 4, ymin = -Inf, ymax = Inf, fill = "green", alpha = 1/5)
到目前为止我所拥有的：
我想绘制 1 个横跨刻面边缘的大矩形，如下所示：
有没有办法使用内置ggplot2代码或使用ggforce或我必须搞砸grid？我理想的用例仍然允许我拥有myPlot一个 ggplot 对象，这就是为什么在此之前我一直避免使用任何复杂的网格内容。
一种使用grid函数来编辑您的plot.
在视口中绘制矩形很容易grid。是否可以构建一个grid完全覆盖 ggplot 面板集的视口？答案是“是”。绘制矩形的诀窍是将 x 轴“原生”坐标从ggplot_build信息中获取到网格视口中。
library(ggplot2)
library(grid)
plot <- ggplot(mpg, aes(displ, hwy)) +
geom_point() +
facet_grid(class ~ .)
plot
# Construct a grid.layout that is the same as the ggplot layout
gt = ggplotGrob(plot)
lay = grid.layout(nrow = length(gt$heights), ncol = length(gt$widths),
widths = gt$widths, heights = gt$heights)
# Push to this viewport
pushViewport(viewport(layout = lay))
# Within the layout, push to a viewport that spans the plot panels.
pos = gt$layout[grep("panel", gt$layout$name), c("t", "l")] # Positions of the panels
pushViewport(viewport(layout.pos.col = pos$l, layout.pos.row = min(pos$t):max(pos$t)))
# Get the limits of the ggplot's x-scale, including any expansion.
## For ggplot ver 2.2.1
# x.axis.limits = ggplot_build(plot)$layout$panel_ranges[[1]][["x.range"]]
## For ver 3.0.0
# axis.limits = ggplot_build(plot)$layout$panel_params[[1]]$x.range
# But possibly the following will be more immune to future changes to ggplot
x.axis.limits = summarise_layout(ggplot_build(plot))[1, c('xmin', 'xmax')]
# Set up a data viewport,
# so that the x-axis units are, in effect, "native",
# but y-axis units are, in effect, "npc".
# And push to the data viewport.
pushViewport(dataViewport(yscale = c(0, 1),
xscale = x.axis.limits))
# Draw the rectangle
grid.rect(x = 3, y = 0,
width = 1, height = 1,
just = c("left", "bottom"), default.units = "native",
gp = gpar(fill = "green", col = "transparent", alpha = .2))
# Back to the root viewport
upViewport(0)
