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Discrete arrow scales

Source: R/scale_arrow.R
discrete_arrow_scales.Rd

These scales can map discrete input to various sorts of arrow shapes. The arrow head, arrow fins and middle arrows have separate scales.

Usage

scale_arrow_head_discrete(values = NULL, aesthetics = "arrow_head", ...)

scale_arrow_fins_discrete(values = NULL, aesthetics = "arrow_fins", ...)

scale_arrow_mid_discrete(values = NULL, aesthetics = "arrow_mid", ...)

Arguments

values

One of the following:

  • A <character> vector of arrow function names, without the arrow_-prefix, such as "head_wings" or "fins_line".

  • An unnested <list>, possibly mixed <list>, containing any of the following elements:

    • A single <character> as described above.

    • A <function> that when called without any arguments produces a 2-column <matrix> that can be used as an arrow.

    • A 2-column <matrix> giving a polygon to use as an arrow.

  • NULL, which defaults to a built-in palette with a maximum of 3 arrows.

aesthetics

The names of the aesthetics that this scale works with

...

Arguments passed on to ggplot2::discrete_scale

scale_name

[Deprecated] The name of the scale that should be used for error messages associated with this scale.

palette

A palette function that when called with a single integer argument (the number of levels in the scale) returns the values that they should take (e.g., scales::pal_hue()).

name

The name of the scale. Used as the axis or legend title. If waiver(), the default, the name of the scale is taken from the first mapping used for that aesthetic. If NULL, the legend title will be omitted.

breaks

One of:

  • NULL for no breaks

  • waiver() for the default breaks (the scale limits)

  • A character vector of breaks

  • A function that takes the limits as input and returns breaks as output. Also accepts rlang lambda function notation.

labels

One of:

  • NULL for no labels

  • waiver() for the default labels computed by the transformation object

  • A character vector giving labels (must be same length as breaks)

  • An expression vector (must be the same length as breaks). See ?plotmath for details.

  • A function that takes the breaks as input and returns labels as output. Also accepts rlang lambda function notation.

limits

One of:

  • NULL to use the default scale values

  • A character vector that defines possible values of the scale and their order

  • A function that accepts the existing (automatic) values and returns new ones. Also accepts rlang lambda function notation.

expand

For position scales, a vector of range expansion constants used to add some padding around the data to ensure that they are placed some distance away from the axes. Use the convenience function expansion() to generate the values for the expand argument. The defaults are to expand the scale by 5% on each side for continuous variables, and by 0.6 units on each side for discrete variables.

na.translate

Unlike continuous scales, discrete scales can easily show missing values, and do so by default. If you want to remove missing values from a discrete scale, specify na.translate = FALSE.

na.value

If na.translate = TRUE, what aesthetic value should the missing values be displayed as? Does not apply to position scales where NA is always placed at the far right.

drop

Should unused factor levels be omitted from the scale? The default, TRUE, uses the levels that appear in the data; FALSE includes the levels in the factor. Please note that to display every level in a legend, the layer should use show.legend = TRUE.

guide

A function used to create a guide or its name. See guides() for more information.

position

For position scales, The position of the axis. left or right for y axes, top or bottom for x axes.

call

The call used to construct the scale for reporting messages.

super

The super class to use for the constructed scale

Value

A <Scale> that can be added to a plot.

Examples

# A standard arrow plot
p <- ggplot(whirlpool(5), aes(x, y, colour = group)) +
  geom_arrow(length_head = 10, length_fins = 10, arrow_head = NULL)

# A character vector naming arrow shapes as arrow head scale
p + aes(arrow_head = group) +
  scale_arrow_head_discrete(values = c(
      "head_wings", "head_line", "head_minimal", "fins_line", "fins_feather"
  ))


# A mixed list with arrows as arrow fins scale
p + aes(arrow_fins = group) +
  scale_arrow_fins_discrete(values = list(
    "head_wings",              # Using a character
    arrow_head_wings(20, 100), # Using an arrow function
    NULL,                      # No arrow
    matrix(c(1, 0, 0, 0, 0.5, -0.5), ncol = 2), # A matrix
    "fins_feather"
  ))