geom_grob: Inset graphical objects

In ggpp: Grammar Extensions to 'ggplot2'

Inset graphical objects

Description

geom_grob and geom_grob_npc add Grobs as insets to the ggplot using syntax similar to that of geom_text, geom_text_s and geom_text_npc. In most respects they behave as any other ggplot geometry: they add a layer containing one or more grobs and grouping and faceting works as usual. The most common use of geom_grob is to add data labels that are graphical objects rather than text. geom_grob_npc is used to add grobs as annotations to plots, but contrary to layer function annotate(), geom_grob_npc is data driven and respects grouping and facets, thus plot insets can differ among panels. Of these two geoms only geom_grob supports the plotting of segments, as geom_grob_npc uses a coordinate system that is unrelated to data units and data.

Usage

geom_grob(
  mapping = NULL,
  data = NULL,
  stat = "identity",
  position = "identity",
  ...,
  nudge_x = 0,
  nudge_y = 0,
  default.colour = "black",
  default.color = default.colour,
  colour.target = "segment",
  color.target = colour.target,
  default.alpha = 1,
  alpha.target = "segment",
  add.segments = TRUE,
  box.padding = 0.25,
  point.padding = 1e-06,
  segment.linewidth = 0.5,
  min.segment.length = 0,
  arrow = NULL,
  na.rm = FALSE,
  show.legend = FALSE,
  inherit.aes = FALSE
)

geom_grob_npc(
  mapping = NULL,
  data = NULL,
  stat = "identity",
  position = "identity",
  ...,
  na.rm = FALSE,
  show.legend = FALSE,
  inherit.aes = FALSE
)

Arguments

mapping	The aesthetic mapping, usually constructed with aes. Only needs to be set at the layer level if you are overriding the plot defaults.
data	A layer specific dataset - only needed if you want to override the plot defaults.
stat	The statistical transformation to use on the data for this layer, as a string.
position	Position adjustment, either as a string, or the result of a call to a position adjustment function.
...	other arguments passed on to layer. This can include aesthetics whose values you want to set, not map. See layer for more details.
nudge_x, nudge_y	Horizontal and vertical adjustments to nudge the starting position of each text label. The units for nudge_x and nudge_y are the same as for the data units on the x-axis and y-axis.
default.colour, default.color	A colour definition to use for elements not targeted by the colour aesthetic.
colour.target, color.target	A vector of character strings; "all", "text", "box" and "segment" or "none".
default.alpha	numeric in [0..1] A transparency value to use for elements not targeted by the alpha aesthetic.
alpha.target	A vector of character strings; "all", "text", "segment", "box", "box.line", and "box.fill" or "none".
add.segments	logical Display connecting segments or arrows between original positions and displaced ones if both are available.
box.padding, point.padding	numeric By how much each end of the segments should shortened in mm.
segment.linewidth	numeric Width of the segments or arrows in mm.
min.segment.length	numeric Segments shorter that the minimum length are not rendered, in mm.
arrow	specification for arrow heads, as created by arrow
na.rm	If FALSE (the default), removes missing values with a warning. If TRUE silently removes missing values.
show.legend	logical. Should this layer be included in the legends? NA, the default, includes if any aesthetics are mapped. FALSE never includes, and TRUE always includes.
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

You can modify the size of insets with the vp.width and vp.height aesthetics. These can take a number between 0 (smallest possible inset) and 1 (whole plotting area width or height). The default value for for both of these aesthetics is 1/5. Thus, in contrast to geom_text, geom_label, geom_text_s and geom_label_s the size of the insets remains the same relative to the size of the plotting area irrespective of the size the plot is rendered at. The aspect ratio of insets is preserved and size is adjusted until the whole inset fits within the viewport.

By default geom_grob uses position_nudge_center and justification "position", while geom_grob_npc uses position_nudge and justification "inward". In contrast to position_nudge, position_nudge_center and all other position functions defined in packages 'ggpp' keep the original coordinates thus allowing the plotting of connecting segments and arrows.

This geom_grob and geom_grob_npc require the use tibbles as argument for data, as the grobs should be stored as a list of graphics objects ("grob") to be mapped to the label aesthetic.

The x and y aesthetics determine the position of the whole inset grob, similarly to that of a text label, justification is interpreted as indicating the position of the grob with respect to its x and y coordinates in the data, and angle is used to rotate the grob as a whole.

Value

A plot layer instance.

Plot boundaries and clipping

The "width" and "height" of an inset as for a text element are 0, so stacking and dodging inset plots will not work by default, and axis limits are not automatically expanded to include all inset plots. Obviously, insets do have height and width, but they are physical units, not data units. The amount of space they occupy on the main plot is not constant in data units of the base plot: when you modify scale limits, inset plots stay the same size relative to the physical size of the base plot.

Alignment

You can modify text alignment with the vjust and hjust aesthetics. These can either be a number between 0 (right/bottom) and 1 (top/left) or a character ("left", "middle", "right", "bottom", "center", "top"). In addition, you can use special alignments for justification including "position", "inward" and "outward". Inward always aligns text towards the center of the plotting area, and outward aligns it away from the center of the plotting area. If tagged with _mean or _median (e.g., "outward_mean") the mean or median of the data in the panel along the corresponding axis is used as center. If the characters following the underscore represent a number (e.g., "outward_10.5") the reference point will be this value in data units. Position justification is computed based on the direction of the displacement of the position of the label so that each individual text or label is justified outwards from its original position. The default justification is "position".

If no position displacement is applied, or a position function defined in 'ggplot2' is used, these geometries behave similarly to the corresponding ones from package 'ggplot2' with a default justification of 0.5 and no segment drawn.

Position functions

Many layer functions from package 'ggpp' are designed to work seamlessly with position functions that keep, rather than discard, the original x and y positions in data when computing a new displaced position. See position_nudge_keep, position_dodge_keep, position_jitter_keep, position_nudge_center, position_nudge_line, position_nudge_to, position_dodgenudge, position_jitternudge, and position_stacknudge for examples and details of their use.

Note

The insets are stored nested within the main ggplot object and contain their own copy of the data, and are rendered as grid grobs as normal ggplots at the time the main ggplot is rendered. They can have different themes.

Use annotate as redefined in 'ggpp' when adding insets as annotations (automatically available unless 'ggpp' is not attached). annotate cannot be used with the npcx and npcy pseudo-aesthetics.

References

The idea of implementing a geom_custom() for grobs has been discussed as an issue at https://github.com/tidyverse/ggplot2/issues/1399.

See Also

grid-package, geom_text, and other documentation of package 'ggplot2'.

Examples

library(tibble)
df <- tibble(x = 2, y = 15, grob = list(grid::circleGrob(r = 0.2)))

# without nudging no segments are drawn
ggplot(data = mtcars,
       aes(wt, mpg)) +
  geom_point(aes(colour = factor(cyl))) +
  geom_grob(data = df,
            aes(x, y, label = grob))

# with nudging segments are drawn
ggplot(data = mtcars,
       aes(wt, mpg)) +
  geom_point(aes(colour = factor(cyl))) +
  geom_grob(data = df,
            aes(x, y, label = grob),
            nudge_x = 0.5,
            colour = "red",
            hjust = 0.5,
            vjust = 0.5)

ggplot(data = mtcars,
       aes(wt, mpg)) +
  geom_point(aes(colour = factor(cyl))) +
  geom_grob(data = df,
            aes(x, y, label = grob),
            nudge_x = 0.5,
            colour = "red",
            colour.target = "none",
            hjust = 0.5,
            vjust = 0.5)

# with nudging plotting of segments can be disabled
ggplot(data = mtcars,
       aes(wt, mpg)) +
  geom_point(aes(colour = factor(cyl))) +
  geom_grob(data = df,
            aes(x, y, label = grob),
            add.segments = FALSE,
            nudge_x = 0.5,
            hjust = 0.5,
            vjust = 0.5)

ggpp documentation built on Nov. 8, 2023, 1:10 a.m.