第 5 章 导出图片

5.1 R语言通用图片保存函数write_fig

你是否厌倦了R语言每次保存图件时必须的三个步骤：先开dev，然后print图件，最后再dev.off? 你是否经常记混不同图片保存函数的参数？R语言中，图片保存函数众多，但不同的函数参数不尽相同。

CairoPDF(file = ifelse(onefile, "Rplots.pdf","Rplot%03d.pdf"),
         width = 6, height = 6, onefile = TRUE, family = "Helvetica",
         title = "R Graphics Output", fonts = NULL, version = "1.1",
         paper = "special", encoding, bg, fg, pointsize, pagecentre)
tiff(filename = "Rplot%03d.tif",
     width = 480, height = 480, units = "px", pointsize = 12,
     compression = c("none", "rle", "lzw", "jpeg", "zip", "lzw+p", "zip+p"),
     bg = "white", res = NA, family = "", restoreConsole = TRUE,
     type = c("windows", "cairo"), antialias)
CairoPNG, jpeg, svg, win.metafile, ...

今天要介绍的Ipaper::write_fig将这些图片保存函数统一起来。write_fig支持保存成pdf, tif, png, jpg, svg和emf等任何你需要格式的图件。生成不同类型的图片，不需要修改参数，只需要动动手指修改输出文件名的后缀即可。

安装方法

remotes::install_github("rpkgs/Ipaper")

使用说明 该函数的使用方法如下：

library(Ipaper)
# ?write_fig # find the document
write_fig(
  p,
  file = "Rplot.pdf",
  width = 10,
  height = 5,
  devices = NULL,
  res = 300,
  show = TRUE
)

参数(arguments)

  • p: 可以是ggplot、lattice、grid或者基础绘图expression
  • file: 输出图件的文件名
  • width: 图片宽度（英寸in），默认10in
  • height: 图片高度（英寸in），默认5in
  • devices: 可以是以下的一种或多种c(“pdf,” “tif,” “tiff,” “png,” “jpg,” “svg,” “emf”)。如果没有提供，则从file中获取文件后缀。file无后缀，则默认为pdf.
  • res: 图形分辨率，默认为论文格式要求300dpi。
  • show: 布尔型，保存完后是否打开图件？

下面以不同的类型p的说明该函数的调用方法

5.2 ggplot

library(ggplot2)
p <- ggplot(mpg, aes(class, hwy)) + geom_boxplot2()
p

write_fig图片默认保存的是pdf格式，pdf格式的图片是矢量图形，高清、易后期编辑是他的优点。如果show=TRUE，然后该函数会使用SumatraPDF打开输出的pdf。SumatraPDF是rstudio自带的pdf阅读器。SumatraPDF不像adobe或福昕，它不会锁死pdf文件。如果你想修改图片，重新导出pdf，你不需要事先在SumatraPDF中关掉重名的旧文件。

write_fig(p, "fig_ggplot.pdf", show = FALSE)

如果你想保存其他格式的图片，只需将“fig_ggplot.pdf”的后缀pdf改成对应新图片类型的后缀即可，以tif为例：

write_fig(p, "fig_ggplot.tif", show = FALSE)

如果你不想修改file名，你可以指定devices：

write_fig(p, "fig_ggplot.pdf", show = FALSE, devices = "tif")

一次保存多种类型的图片：

write_fig(p, "fig_ggplot.pdf", show = FALSE, devices = c("jpg", "png", "svg", "pdf", "tif", "emf"))

5.3 lattice and grid

lattice和grid与ggplot类型的调用格式一致。

library(lattice)
x <- seq(pi/4, 5 * pi, length.out = 100)
y <- seq(pi/4, 5 * pi, length.out = 100)
r <- as.vector(sqrt(outer(x^2, y^2, "+")))
grid <- expand.grid(x=x, y=y)
grid$z <- cos(r^2) * exp(-r/(pi^3))
p <- levelplot(z~x*y, grid, cuts = 50, scales=list(log="e"), xlab="",
          ylab="", main="Weird Function", sub="with log scales",
          colorkey = FALSE, region = TRUE)
p

write_fig(p, "fig_lattice", show = FALSE)

grid类型

g <- grid::circleGrob()
grid::grid.draw(g)

write_fig(g, "fig_grid", show = FALSE)

5.4 基础绘图语法

对于基础绘图语法，你需要使用expression将其包裹起来。

write_fig(expression({
    rx <- range(x <- 10*1:nrow(volcano))
    ry <- range(y <- 10*1:ncol(volcano))
    ry <- ry + c(-1, 1) * (diff(rx) - diff(ry))/2
    tcol <- terrain.colors(12)
    # par(opar); 
    # opar <- par(pty = "s", bg = "lightcyan")
    plot(x = 0, y = 0, type = "n", xlim = rx, ylim = ry, xlab = "", ylab = "")
    u <- par("usr")
    rect(u[1], u[3], u[2], u[4], col = tcol[8], border = "red")
    contour(x, y, volcano, col = tcol[2], lty = "solid", add = TRUE,
            vfont = c("sans serif", "plain"))
    title("A Topographic Map of Maunga Whau", font = 4)
    abline(h = 200*0:4, v = 200*0:4, col = "lightgray", lty = 2, lwd = 0.1)
}), "fig_expr.pdf", show = FALSE)
#> expression({
#>     rx <- range(x <- 10 * 1:nrow(volcano))
#>     ry <- range(y <- 10 * 1:ncol(volcano))
#>     ry <- ry + c(-1, 1) * (diff(rx) - diff(ry))/2
#>     tcol <- terrain.colors(12)
#>     plot(x = 0, y = 0, type = "n", xlim = rx, ylim = ry, xlab = "", 
#>         ylab = "")
#>     u <- par("usr")
#>     rect(u[1], u[3], u[2], u[4], col = tcol[8], border = "red")
#>     contour(x, y, volcano, col = tcol[2], lty = "solid", add = TRUE, 
#>         vfont = c("sans serif", "plain"))
#>     title("A Topographic Map of Maunga Whau", font = 4)
#>     abline(h = 200 * 0:4, v = 200 * 0:4, col = "lightgray", lty = 2, 
#>         lwd = 0.1)
#> })