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Vectors from the origin

Source: R/geom-vector.r
geom_vector.Rd

geom_vector() renders arrows from the origin to points, optionally with text radiating outward.

Usage

geom_vector(
  mapping = NULL,
  data = NULL,
  stat = "identity",
  position = "identity",
  arrow = default_arrow,
  lineend = "round",
  linejoin = "mitre",
  vector_labels = TRUE,
  ...,
  label.colour = NULL,
  label.color = NULL,
  label.alpha = NULL,
  parse = FALSE,
  check_overlap = FALSE,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE
)

Arguments

mapping

Set of aesthetic mappings created by aes(). If specified and inherit.aes = TRUE (the default), it is combined with the default mapping at the top level of the plot. You must supply mapping if there is no plot mapping.

data

The data to be displayed in this layer. There are three options:

If NULL, the default, the data is inherited from the plot data as specified in the call to ggplot().

A data.frame, or other object, will override the plot data. All objects will be fortified to produce a data frame. See fortify() for which variables will be created.

A function will be called with a single argument, the plot data. The return value must be a data.frame, and will be used as the layer data. A function can be created from a formula (e.g. ~ head(.x, 10)).

stat

The statistical transformation to use on the data for this layer. When using a geom_*() function to construct a layer, the stat argument can be used the override the default coupling between geoms and stats. The stat argument accepts the following:

  • A Stat ggproto subclass, for example StatCount.

  • A string naming the stat. To give the stat as a string, strip the function name of the stat_ prefix. For example, to use stat_count(), give the stat as "count".

  • For more information and other ways to specify the stat, see the layer stat documentation.

position

A position adjustment to use on the data for this layer. This can be used in various ways, including to prevent overplotting and improving the display. The position argument accepts the following:

  • The result of calling a position function, such as position_jitter(). This method allows for passing extra arguments to the position.

  • A string naming the position adjustment. To give the position as a string, strip the function name of the position_ prefix. For example, to use position_jitter(), give the position as "jitter".

  • For more information and other ways to specify the position, see the layer position documentation.

arrow

Specification for arrows, as created by grid::arrow(), or else NULL for no arrows.

lineend

Line end style (round, butt, square).

linejoin

Line join style (round, mitre, bevel).

vector_labels

Logical; whether to include labels radiating outward from the vectors.

...

Additional arguments passed to ggplot2::layer().

label.colour, label.color, label.alpha

Default aesthetics for labels. Set to NULL to inherit from the data's aesthetics.

parse

If TRUE, the labels will be parsed into expressions and displayed as described in ?plotmath.

check_overlap

If TRUE, text that overlaps previous text in the same layer will not be plotted. check_overlap happens at draw time and in the order of the data. Therefore data should be arranged by the label column before calling geom_text(). Note that this argument is not supported by geom_label().

na.rm

Passed to ggplot2::layer().

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. It can also be a named logical vector to finely select the aesthetics to display.

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().

Value

A ggproto layer.

Details

Vectors are positions relative to some common reference point, in this case the origin; they comprise direction and magnitude. Vectors are usually represented with arrows rather than markers (points).

Vectors are commonly used to represent numerical variables in biplots, as by Gabriel (1971) and Greenacre (2010). Gardner & le Roux (2002) refer to these as Gabriel biplots. This layer, with optional radiating text labels, is adapted from ggbiplot() in the off-CRAN extensions of the same name (Vu, 2014; Telford, 2017; Gegzna, 2018).

Biplot layers

ggbiplot() uses ggplot2::fortify() internally to produce a single data frame with a .matrix column distinguishing the subjects ("rows") and variables ("cols"). The stat layers stat_rows() and stat_cols() simply filter the data frame to one of these two.

The geom layers geom_rows_*() and geom_cols_*() call the corresponding stat in order to render plot elements for the corresponding factor matrix. geom_dims_*() selects a default matrix based on common practice, e.g. points for rows and arrows for columns.

Aesthetics

geom_vector() understands the following aesthetics (required aesthetics are in bold):

  • x

  • y

  • alpha

  • colour

  • linetype

  • label

  • size

  • angle

  • hjust

  • vjust

  • family

  • fontface

  • lineheight

  • group

References

Gabriel KR (1971) "The biplot graphic display of matrices with application to principal component analysis". Biometrika 58(3), 453–467. doi:10.1093/biomet/58.3.453

Greenacre MJ (2010) Biplots in Practice. Fundacion BBVA, ISBN: 978-84-923846. https://www.fbbva.es/microsite/multivariate-statistics/biplots.html

Gardner S, le Roux N (2002) "Biplot Methodology for Discriminant Analysis Based upon Robust Methods and Principal Curves". Classification, Clustering, and Data Analysis: Recent Advances and Applications: 169–176. https://link.springer.com/chapter/10.1007/978-3-642-56181-8_18

Vincent Q. Vu (2014). ggbiplot: A 'ggplot2' based biplot. R package version 0.55. https://github.com/vqv/ggbiplot, experimental branch

Richard J Telford (2017). ggbiplot: A 'ggplot2' based biplot. R package version 0.6. https://github.com/richardjtelford/ggbiplot (fork), experimental branch

Vilmantas Gegzna (2018). ggbiplot: A 'ggplot2' based biplot. R package version 0.55. https://github.com/forked-packages/ggbiplot (fork), experimental branch

See also

Other geom layers: geom_axis(), geom_bagplot(), geom_interpolation(), geom_isoline(), geom_lineranges(), geom_origin(), geom_rule(), geom_text_radiate()

Examples

# multidimensional scaling of covariances
ability.cov$cov |> 
  cov2cor() |>
  eigen() |> getElement("vectors") |> 
  as.data.frame() |> 
  transform(test = rownames(ability.cov$cov)) ->
  ability_cor_eigen
ability_cor_eigen |> 
  ggplot(aes(-V1, V2, label = test)) +
  coord_square() + theme_void() +
  geom_vector(check_overlap = TRUE) +
  scale_y_continuous(expand = expansion(mult = .2)) +
  ggtitle("Ability and intelligence test covariances")

# multidimensional scaling of correlations
ability.cov$cov |> 
  eigen() |> getElement("vectors") |> 
  as.data.frame() |> 
  transform(test = rownames(ability.cov$cov)) ->
  ability_cor_eigen
ability_cor_eigen |> 
  ggplot(aes(-V1, -V2, label = test)) +
  coord_square() + theme_void() +
  geom_vector(check_overlap = TRUE) +
  geom_unit_circle() +
  expand_limits(x = c(-1, 1), y = c(-1, 1)) +
  ggtitle("Ability and intelligence test covariances")