ggsave_fitmax: Save ggplot to correctly-shaped image file

In infotroph/DeLuciatoR: Make R Plots Match DeLucia Publication Specs

Description

When a ggplot has a fixed panel aspect ratio, it can be a pain to find the right dimensions for the whole plot (including axes, margins, legends, etc) when saving it to a fixed-size graphical device. ggsave_fitmax takes a ggplot object and saves it as the largest image that fits inside the specified maximum height and width.

Usage

	ggsave_fitmax(filename, plot=last_plot(), 
		maxheight=7, maxwidth=maxheight,
		units="in", ...)

Arguments

filename	Name for the output image. By default the image format is guesssed from the file extension, but this can be overridden by specifying a value for device. See ggsave for details.
plot	A ggplot or gtable object. Defaults to the last plot displayed.
maxheight, maxwidth	Numeric, giving largest allowable dimensions of the plot. The final image will exactly match one of these and will not exceed the other.
units	One of "in", "cm", "mm", giving units for the dimensions. Note that "px" does not work.
...	Other arguments passed to ggsave, notably including dpi (to set pixel resolution of the output image) and limitsize (set to FALSE if you really do want an image larger than 50 inches).

Details

This is a convenience function that wraps two distinct steps: Looking up the plot dimensions using get_dims, and saving the image using ggsave. If you need more flexibility in either step, skip this wrapper and call get_dims directly, then pass the computed dimensions to your favorite graphics device. See the examples in get_dims for an example.

The dimension lookup was motivated by the difficulty of predicting image height & width when the panels have a fixed aspect ratio, but this wrapper should work as a one-call plotting command for plots with unconstrained ratios as well. Please report any that don't work.

Note

For pixel-based formats such as PNG, the conversion between pixels and physical inch/mm dimensions is more complicated that it sounds. In particular, some image viewers will treat a high-dpi image as a very large but low-dpi image. See the "Details" section of png for more, but the upshot is that ggsave_fitmax always produces a raster image containing the right number of pixels to produce the requested physical dimensions if displayed at the specified dpi.

Author(s)

Chris Black <[e-mail]>

Examples

## Not run: 
a=ggplot(mtcars, aes(wt,mpg))+geom_point()+theme(aspect.ratio=0.75)

# Saves a.pdf at 10.55 x 8 inches
ggsave_fitmax(filename="a.pdf", plot=a, maxheight=8, maxwidth=12)

# Saves a.png at 3163 x 2400 px 
# == (nominally!) 10.55 x 8 inches at 300 ppi.
ggsave_fitmax(filename="a.png", plot=a, maxheight=8, maxwidth=12)

# Saves aa.jpg at 1181 x 900 px
# == 7.8 x 6 inches at 150 ppi... or 3.9 x 3 inches at 300 ppi, or 16.4 x 12.5 at 72 ppi, or...
ggsave_fitmax(filename="aa.jpg", plot=a, maxheight=6, maxwidth=9, dpi=150)


## End(Not run)

infotroph/DeLuciatoR documentation built on May 30, 2020, 10:28 p.m.