R：ggplot2使用facet_wrap设置中间的最后一个图

Question

我正在尝试使用facet_wrap创建一些多图。但是，我不确定是否适合我的图表。这是一个简短的可复制示例：

 ggplot(airquality, aes(x = Day, y = Temp)) +
  facet_wrap(~Month) + 
  geom_line()

这将在此处生成该图：

是否可以使用facet_wrap方法“居中”第二行中的两个图？ 请注意，我不想对图进行重新排序，只想将第二行居中

Answer 1

@Tjebo关于使用cowplot的建议将起作用：

p <- ggplot(mapping = aes(x = Day, y = Temp)) +
  facet_wrap(~Month) + 
  geom_line()

cowplot::plot_grid(
  p %+% subset(airquality, Month < 8),
  p %+% subset(airquality, Month > 7),
  nrow = 2
)

Answer 2

您还可以考虑使用egg软件包中的函数set_panel_size，该函数可让您将多个绘图的面板大小（宽度，高度）设置为绝对测量值，有关更多信息，请参见this vignette详细信息。

使用Axeman的代码创建绘图

library(egg)
library(gridExtra)
p <- ggplot(mapping = aes(x = Day, y = Temp)) +
  facet_wrap(~Month) + 
  geom_line()

p1 <- p %+% subset(airquality, Month < 8) + labs(x = NULL)
p2 <- p %+% subset(airquality, Month > 7)

现在在指定面板尺寸后使用grid.arrange布置图

grid.arrange(grobs = lapply(
  list(p1, p2),
  set_panel_size,
  width = unit(5, "cm"),
  height = unit(4, "cm")
))

Answer 3

以防万一有人想知道如何从头开始在网格中做这件事...

library(ggplot2)
library(dplyr)
library(grid)

vps <- c("top_left", "top_mid", "top_right", "bottom_left", "bottom_right")

main_vp  <- vpTree(viewport(name = "main"), vpList(
              viewport(x = 1/6, y = 0.75, width = 1/3, height = 0.5, name = vps[1]),
              viewport(x = 3/6, y = 0.75, width = 1/3, height = 0.5, name = vps[2]),
              viewport(x = 5/6, y = 0.75, width = 1/3, height = 0.5, name = vps[3]),
              viewport(x = 1/3, y = 0.25, width = 1/3, height = 0.5, name = vps[4]),
              viewport(x = 2/3, y = 0.25, width = 1/3, height = 0.5, name = vps[5])))

grid.newpage()
pushViewport(main_vp)

plots <- lapply(1:5, function(i){ 
  seekViewport(vps[i])
  invisible(grid.draw(ggplotGrob(
    
    ggplot(filter(airquality, Month == levels(as.factor(airquality$Month))[i]), 
           mapping = aes(Day, Temp)) + 
      geom_line() + 
      facet_grid(.~Month)
    
)))})

^{由reprex package（v0.3.0）于2020-07-03创建}