使用给定的宽高比保存绘图

Question

我正在使用非常棒的库ggplot2.我想通过使用如何设置绘图的纵横比coord_fixed.现在,我想将绘图保存为具有指定宽度(例如10 cm)的PDF,并计算所需的高度.我没弄明白如何实现这一目标.这甚至可能吗？

Answer 1

您可以使用网格函数来计算ggplot grob的完整大小,但有(编辑:至少)两个警告:

• 将打开一个额外的设备窗口,进行单位转换

• 默认情况下,绘图面板大小为0,因为它意味着根据它所在的设备(视口)即时计算,而不是相反.

话虽这么说,以下函数试图打开一个完全符合ggplot的设备,

library(ggplot2)
library(grid)

sizeit <- function(p, panel.size = 2, default.ar=1){

  gb <- ggplot_build(p)
  # first check if theme sets an aspect ratio
  ar <- gb$plot$coordinates$ratio

  # second possibility: aspect ratio is set by the coordinates, which results in 
  # the use of 'null' units for the gtable layout. let's find out
  g <- ggplot_gtable(gb)
  nullw <- sapply(g$widths, attr, "unit")
  nullh <- sapply(g$heights, attr, "unit")

  # ugly hack to extract the aspect ratio from these weird units
  if(any(nullw == "null"))
    ar <- unlist(g$widths[nullw == "null"]) / unlist(g$heights[nullh == "null"])

  if(is.null(ar)) # if the aspect ratio wasn't specified by the plot
       ar <- default.ar

  # ensure that panel.size is always the larger dimension
  if(ar <= 1 ) panel.size <- panel.size / ar

  g$fullwidth <- convertWidth(sum(g$widths), "in", valueOnly=TRUE) + 
    panel.size
  g$fullheight <- convertHeight(sum(g$heights), "in", valueOnly=TRUE) + 
    panel.size / ar

  class(g) <- c("sizedgrob", class(g))
  g
}


print.sizedgrob <- function(x){
  # note: dev.new doesn't seem to respect those parameters
  # when called from Rstudio; in this case it 
  # may be replaced by x11 or quartz or ...
  dev.new(width=x$fullwidth, height=x$fullheight)
  grid.draw(x)
}


p1 <- ggplot(mtcars, aes(x = wt, y = mpg)) + geom_point() + coord_fixed() +
  theme(plot.background = element_rect(colour = "red"))

p2 <- p1 + aes(x = mpg, y = wt)

# need for an explicit dummy device open, otherwise it's a bit off
# for no apparent reason that I can understand
dev.new() 

sizeit(p1, 0.1)

sizeit(p2, 2)

Answer 2

根据 baptiste 的回答，我精简了他的代码以返回 geotheory 建议的纵横比。这对我来说更方便，因为我想要一个固定的宽度或高度，并且还通过现有的包装函数传递所有内容，该函数还将字体添加到我的 pdf 中。

哦，如果您使用了 facet，则需要手动考虑它们。按行除以列乘以。不知道有没有更好的方法......

ggGetAr <- function(p, default.ar=-1){

    gb <- ggplot_build(p)
    # first check if theme sets an aspect ratio
    ar <- gb$plot$coordinates$ratio

    # second possibility: aspect ratio is set by the coordinates, which results in 
    # the use of 'null' units for the gtable layout. let's find out
    g <- ggplot_gtable(gb)
    nullw <- sapply(g$widths, attr, "unit")
    nullh <- sapply(g$heights, attr, "unit")

    # ugly hack to extract the aspect ratio from these weird units
    if(any(nullw == "null"))
        ar <- unlist(g$widths[nullw == "null"]) / unlist(g$heights[nullh == "null"])

    if(is.null(ar)) # if the aspect ratio wasn't specified by the plot
        ar <- default.ar

    ar[1]
}