Saving plots: ggsave

Mix.install([
  {:giggly, path: Path.join(__DIR__, "..")},
  {:kino, "~> 0.19"}
  ])

About this notebook

This notebook follows the examples on ggplot2's reference page for ggsave(), in the order the page gives them. Each example shows ggplot2's code first and then Giggly's. An example Giggly cannot draw yet keeps its ggplot2 code and names what it is waiting for, so the page is also a list of what remains.

ggsave() writes a plot to a file: by default the last plot displayed, at the size of the current graphics device, in a format it guesses from the file name's extension. Giggly has no ggsave(). Building or drawing a Giggly plot has no side effects, so nothing is written to a file and no plot is remembered as the last; Giggly.to_svg/2 returns the drawing as an SVG document, the only format Giggly draws, and saving it is the caller's File.write!/2.

Saving by file name

ggplot(mtcars, aes(mpg, wt)) +
  geom_point()
# here, the device is inferred from the filename extension
ggsave("mtcars.pdf")
ggsave("mtcars.png")

ggplot2 saves the plot just drawn, as a PDF and then as a PNG, each format chosen by the file's extension. Giggly draws SVG only; a plot is saved by writing what Giggly.to_svg/2 returns with File.write!/2.

The size of the drawing

# setting dimensions of the plot
ggsave("mtcars.pdf", width = 4, height = 4)
ggsave("mtcars.pdf", width = 20, height = 20, units = "cm")

Giggly.to_svg/2 takes the drawing's size as its width: and height: options, in pixels.

Options for the device

# passing device-specific arguments to '...'
ggsave("mtcars.pdf", colormodel = "cmyk")

The other arguments go to R's PDF device, here to write the colours as CMYK. Giggly draws SVG only.

Deleting the files

# delete files with base::unlink()
unlink("mtcars.pdf")
unlink("mtcars.png")

This deletes the files the examples above wrote; it uses nothing of ggplot2's.

Naming the format

# specify device when saving to a file with unknown extension
# (for example a server supplied temporary file)
file <- tempfile()
ggsave(file, device = "pdf")
unlink(file)

A temporary file's name has no extension to guess a format from, so device names it. Giggly draws SVG only, so there is no format to choose.

Saving without ggsave()

# save plot to file without using ggsave
p <-
  ggplot(mtcars, aes(mpg, wt)) +
  geom_point()
png("mtcars.png")
print(p)
dev.off()

R opens a graphics device writing to a PNG file, prints the plot to it and closes it. Giggly has no graphics devices: Giggly.to_svg/2 returns the SVG document itself, and the caller writes it where it likes.