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Create a magnified inset of a plot

Source: R/geom-magnify.R, R/geom-magnify-tile.R
geom_magnify.Rd

geom_magnify() creates a magnified inset of part of a ggplot. Optional borders are drawn around the target and inset, along with projection lines from one to the other. from gives the location of the target area, and to gives the location of the inset. Usually, these are specified as c(xmin, xmax, ymin, ymax).

Usage

geom_magnify(
  mapping = NULL,
  data = NULL,
  stat = StatMagnify,
  position = "identity",
  ...,
  shape = c("rect", "ellipse", "outline"),
  expand = 0.1,
  aspect = c("free", "fixed"),
  axes = "",
  proj = c("facing", "corresponding", "single"),
  shadow = FALSE,
  corners = 0,
  colour = "black",
  linetype = 1,
  target.linetype = linetype,
  inset.linetype = linetype,
  proj.linetype = 2,
  alpha = 1,
  linewidth = 0.4,
  proj.fill = NULL,
  plot = NULL,
  shadow.args = list(sigma = 5, colour = "grey40", x_offset = 5, y_offset = 5),
  recompute = FALSE,
  scale.inset = 1,
  proj.combine = TRUE,
  na.rm = FALSE,
  inherit.aes = TRUE
)

geom_magnify_tile(
  mapping = NULL,
  data = NULL,
  stat = StatMagnifyTile,
  position = "identity",
  ...,
  shape = c("rect", "ellipse", "outline"),
  expand = 0.1,
  aspect = c("free", "fixed"),
  axes = "",
  proj = "facing",
  shadow = FALSE,
  corners = 0,
  colour = "black",
  linetype = 1,
  target.linetype = linetype,
  inset.linetype = linetype,
  proj.linetype = 2,
  alpha = 1,
  linewidth = 0.4,
  proj.fill = NULL,
  plot = NULL,
  shadow.args = list(sigma = 5, colour = "grey40", x_offset = 5, y_offset = 5),
  recompute = FALSE,
  scale.inset = 1,
  proj.combine = TRUE,
  na.rm = FALSE,
  inherit.aes = FALSE
)

Arguments

mapping, data, stat, position, ..., na.rm

See e.g. ggplot2::geom_point().

shape

Shape of the area to be magnified. "rect" for a rectangle. "ellipse" for an ellipse. "outline" for the convex hull of points in the target area, or for map polygons.

expand

Number. Expand the target area and inset proportionally by this amount.

aspect

String. "fixed" to fix the aspect ratio (overrides ymax).

axes

String. Which axes to plot in the inset? "", "x", "y" or "xy".

proj

String. What style of projection lines to draw? "facing" (the default), "corresponding" or "single". Can be abbreviated. See below.

shadow

Logical. Draw a shadow behind the inset plot? Requires the "ggfx" package.

corners

Numeric between 0 and 1. Radius of rounded corners for the target area and inset. Only used if shape is "rect". 0.1 is a good starting value.

linetype, colour, alpha, linewidth

Linetype, colour, alpha and linewidth for borders and projection lines.

target.linetype, inset.linetype, proj.linetype

Linetypes for specific components. Set to 0 for no lines.

proj.fill

Colour to fill between the projection lines. NULL for no fill. Add alpha using e.g. scales::alpha(). Ignored when proj = "single".

plot

Ggplot object to plot in the inset. If NULL, defaults to the ggplot object to which geom_magnify() is added.

shadow.args

List. Arguments to ggfx::with_shadow().

recompute

Logical. If TRUE, use lims() to replot the inset. Statistics, e.g. smoothing lines, will be recomputed using only the data in the target area. If FALSE, use coord_cartesian() to replot the inset, keeping all the data.

scale.inset

Length 1 or 2 numeric. Normally, exactly the target area is shown on the inset. Sometimes you may wish to rescale the plot in the inset. Use 2 numbers to scale width and height separately.

proj.combine

Logical. How to draw projection lines when more than one polygon/map area is magnified? FALSE draws one set of projection lines for each area. TRUE draws a single set of lines for all the areas.

inherit.aes

If FALSE, overrides the default aesthetics, rather than combining with them. This is most useful for helper functions that define both data and aesthetics and shouldn't inherit behaviour from the default plot specification, e.g. borders().

Details

Aesthetics

geom_magnify understand the following aesthetics (required aesthetics are in bold):

  • from

  • to

from and to can be vectors of length 4, like list(xmin, xmax, ymin, ymax). These specify the bottom left and top right corners of the target area to magnify, and the area for the magnified inset. The lists can optionally be named: list(xmin = 1, xmax = 2, ymin = 3, ymax = 4).

Note: very early versions of ggmagnify used a different order of coordinates: list(xmin, ymin, xmax, ymax).

Alternatively, from can be:

  • A data frame of points with two columns for x and y, or a grid::grob() object. Points within the grob region (a polygon spanned by the data frame) will be magnified. Points should be on the same scale as the data, with default.units = "native" in the grob. shape will be ignored.

  • A logical vector. Points in the data where from is TRUE will be surrounded by a rectangle, ellipse or outline.

Normally you'll set from and to in the call to geom_magnify(). You can specify them as aesthetics, e.g. if you want different areas per facet. If so, you may need to wrap them in a list() to make sure they are length one per row of data. Only the first row per panel is used. (To magnify multiple areas in one panel, use multiple calls to geom_magnify().)

Shapes

If shape = "ellipse" an elliptical area is magnified. This may not include all points within the target area given by from.

If shape = "outline" then a convex hull will be drawn around points in the target area. This only works if you are using geom_point() or some other geom with aesthetics x and y. If you are plotting a map, then "outline" magnifies exactly the map features selected by from.

Projection lines

  • proj = "corresponding" or "facing" draws projection lines from the corners of the target to the corners of the inset.

    • "corresponding" always projects each corner of the target to the same corner of the inset.

    • "facing" sometimes draws lines between facing corners, when this looks cleaner.

    • For non-rectangular insets, "facing" and "corresponding" are the same.

  • "single" draws a single line from the midpoint of facing sides.

  • To draw no lines, set proj.linetype = 0.

Limitations

  • geom_magnify() uses masks. This requires R version 4.1.0 or higher, and a graphics device that supports masking. If you are using knitr, you may have luck with the ragg_png device. If your device doesn't support masks, only shape = "rect" will work, and the plot inset will not be clipped to the panel area.

  • R graphics devices are not very predictable. My current recommendations are: ragg_png for knitr; cairo_pdf for PDF output; RStudio AGG backend for interactive output. Your mileage may vary.

  • geom_magnify() uses dark magic to deal with faceting. It may break with older, or newer, versions of ggplot2. If you don't need faceting, and want your code to be robust to upgrades, set options(ggmagnify.safe_mode = TRUE) to use slightly less magic.

  • By design, geom_magnify() replots the original plot using new limits. It does not directly copy the target area pixels. The advantage is that you can e.g. add axes, plot points at an appropriate size, zoom in on data that's invisible in the main plot, or recompute derived graphics. If you want an exact pixel-by-pixel copy, use a different tool.

  • geom_magnify() may break with discrete scales. This is a limitation in ggplot2 for now.

  • Find a bug? Report it at https://github.com/hughjonesd/ggmagnify/issues/.

geom_magnify_tile()

geom_magnify_tile() is a version of geom_magnify() which uses different aesthetics. Set x, width, y, height and to_x, to_width to_y, to_height to specify the target and inset location.

Examples

library(ggplot2)
ggp <- ggplot(iris, aes(Sepal.Width, Sepal.Length, colour = Species)) +
         geom_point() + xlim(c(2, 6))
from <- list(2.5, 3.5, 6, 7)
to <- list(4, 6, 5, 7)

# Basic magnification
ggp + geom_magnify(from = from, to = to)


# Convex hull of points
ggp + geom_magnify(aes(from = Species == "setosa"), to = c(3, 5, 6, 8),
                   shape = "outline")


# Order matters

# `geom_magnify()` stores the plot when it is added to it:
ggp +
  scale_color_brewer() +
  geom_magnify(from = from, to = to)


# This will print the inset without the new scale:
ggp +
  geom_magnify(from = from, to = to) +
  scale_color_brewer()


# For more examples see https://github.com/hughjonesd/ggmagnify