Continuous Value Applied to a Discrete Scale

October 16, 2022 Post a Comment

This scale allows ggplot to understand data that has been discretised with some procedure akin to cut and access the underlying continuous values. For a scale that does the opposite (take continuous data and treat them as discrete) see ggplot2::binned_scale().

                          as.discretised_scale              (              scale_function              )              scale_fill_discretised              (              ...,   low              =              "#132B43",   high              =              "#56B1F7",   space              =              "Lab",   na.value              =              "grey50",   guide              =              ggplot2              ::              guide_colorsteps              (even.steps              =              FALSE, show.limits              =              TRUE              ),   aesthetics              =              "fill"              )              scale_fill_divergent_discretised              (              ...,   low              =              scales              ::              muted              (              "blue"              ),   mid              =              "white",   high              =              scales              ::              muted              (              "red"              ),   midpoint              =              0,   space              =              "Lab",   na.value              =              "grey50",   guide              =              ggplot2              ::              guide_colorsteps              (even.steps              =              FALSE, show.limits              =              TRUE              )              )              discretised_scale              (              aesthetics,              scale_name,              palette,   name              =              ggplot2              ::              waiver              (              ),   breaks              =              ggplot2              ::              waiver              (              ),   labels              =              ggplot2              ::              waiver              (              ),   limits              =              NULL,   trans              =              scales              ::              identity_trans              (              ),   na.value              =              NA,   drop              =              FALSE,   guide              =              ggplot2              ::              guide_colorsteps              (even.steps              =              FALSE              ),   position              =              "left",   rescaler              =              scales              ::              rescale,   oob              =              scales              ::              censor,   super              =              ScaleDiscretised              )

Arguments

scale_function

a scale function (e.g. scale_fill_divergent)

...

Arguments passed on to continuous_scale

scale_name

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 numeric vector with values between 0 and 1 returns the corresponding output values (e.g., scales::area_pal()).

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 computed by the transformation object
A numeric vector of positions
A function that takes the limits as input and returns breaks as output (e.g., a function returned by scales::extended_breaks()). Also accepts rlang lambda function notation.

minor_breaks

One of:

NULL for no minor breaks
waiver() for the default breaks (one minor break between each major break)
A numeric vector of positions
A function that given the limits returns a vector of minor breaks. Also accepts rlang lambda function notation.

n.breaks

An integer guiding the number of major breaks. The algorithm may choose a slightly different number to ensure nice break labels. Will only have an effect if breaks = waiver(). Use NULL to use the default number of breaks given by the transformation.

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)
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 range
A numeric vector of length two providing limits of the scale. Use NA to refer to the existing minimum or maximum
A function that accepts the existing (automatic) limits and returns new limits. Also accepts rlang lambda function notation. Note that setting limits on positional scales will remove data outside of the limits. If the purpose is to zoom, use the limit argument in the coordinate system (see coord_cartesian()).

rescaler

A function used to scale the input values to the range [0, 1]. This is always scales::rescale(), except for diverging and n colour gradients (i.e., scale_colour_gradient2(), scale_colour_gradientn()). The rescaler is ignored by position scales, which always use scales::rescale(). Also accepts rlang lambda function notation.

oob

One of:

Function that handles limits outside of the scale limits (out of bounds). Also accepts rlang lambda function notation.
The default (scales::censor()) replaces out of bounds values with NA.
scales::squish() for squishing out of bounds values into range.
scales::squish_infinite() for squishing infinite values into range.

trans

For continuous scales, the name of a transformation object or the object itself. Built-in transformations include "asn", "atanh", "boxcox", "date", "exp", "hms", "identity", "log", "log10", "log1p", "log2", "logit", "modulus", "probability", "probit", "pseudo_log", "reciprocal", "reverse", "sqrt" and "time".

A transformation object bundles together a transform, its inverse, and methods for generating breaks and labels. Transformation objects are defined in the scales package, and are called <name>_trans (e.g., scales::boxcox_trans()). You can create your own transformation with scales::trans_new().

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.

position

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

super

The super class to use for the constructed scale

low

Colours for low and high ends of the gradient.

high

Colours for low and high ends of the gradient.

space

colour space in which to calculate gradient. Must be "Lab" - other values are deprecated.

na.value

Colour to use for missing values

guide

Type of legend. Use "colourbar" for continuous colour bar, or "legend" for discrete colour legend.

aesthetics

Character string or vector of character strings listing the name(s) of the aesthetic(s) that this scale works with. This can be useful, for example, to apply colour settings to the colour and fill aesthetics at the same time, via aesthetics = c("colour", "fill").

mid

colour for mid point

midpoint

The midpoint (in data value) of the diverging scale. Defaults to 0.

scale_name

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 numeric vector with values between 0 and 1 returns the corresponding output values (e.g., scales::area_pal()).

name

breaks

One of:

NULL for no breaks
waiver() for the default breaks computed by the transformation object
A numeric vector of positions
A function that takes the limits as input and returns breaks as output (e.g., a function returned by scales::extended_breaks()). 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)
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 range
A numeric vector of length two providing limits of the scale. Use NA to refer to the existing minimum or maximum
A function that accepts the existing (automatic) limits and returns new limits. Also accepts rlang lambda function notation. Note that setting limits on positional scales will remove data outside of the limits. If the purpose is to zoom, use the limit argument in the coordinate system (see coord_cartesian()).

trans

drop

Should unused factor levels be omitted from the scale? The default, TRUE, uses the levels that appear in the data; FALSE uses all the levels in the factor.

position

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

rescaler

oob

One of:

Function that handles limits outside of the scale limits (out of bounds). Also accepts rlang lambda function notation.
The default (scales::censor()) replaces out of bounds values with NA.
scales::squish() for squishing out of bounds values into range.
scales::squish_infinite() for squishing infinite values into range.

super

The super class to use for the constructed scale

Value

A function with the same arguments as scale_function that works with discretised values.

Details

This scale makes it very easy to synchronise the breaks of filled contours and the breaks shown no the colour guide. Bear in mind that when using geom_contour_fill(), the default fill aesthetic (level_mid) is not discretised. To use this scale with that geom, you need to set aes(fill = stat(level)).

Examples

                                                library                  (                  ggplot2                  )                                                  scale_fill_brewer_discretised                  <-                  as.discretised_scale                  (                  scale_fill_distiller                  )                                                                  library                  (                  ggplot2                  )                                                                  # Using the `level` compute aesthetic from `geom_contour_fill()`                                                  # (or ggplot2::geom_contour_filled()), the default scale is discrete.                                                  # This means that you cannot map colours to the underying numbers.                                                  v                  <-                  ggplot                  (                  faithfuld,                  aes                  (                  waiting,                  eruptions, z                  =                  density                  )                  )                                                  v                  +                  geom_contour_fill                  (                  aes                  (fill                  =                  stat                  (                  level                  )                  )                  )                                                                                                                    v                  +                  geom_contour_fill                  (                  aes                  (fill                  =                  stat                  (                  level                  )                  )                  )                  +                                                  scale_fill_discretised                  (                  )                                                                                                                    # The scale can be customised the same as any continuous colour scale                                                  v                  +                  geom_contour_fill                  (                  aes                  (fill                  =                  stat                  (                  level                  )                  )                  )                  +                                                  scale_fill_discretised                  (low                  =                  "#a62100", high                  =                  "#fff394"                  )                                                                                                                    # Setting limits explicitly will truncate the scale                                                  # (if any limit is inside the range of the breaks but doesn't                                                  # coincide with any range, it will be rounded with a warning)                                                  v                  +                  geom_contour_fill                  (                  aes                  (fill                  =                  stat                  (                  level                  )                  )                  )                  +                                                  scale_fill_discretised                  (low                  =                  "#a62100", high                  =                  "#fff394",                                  limits                  =                  c                  (                  0.01,                  0.028                  )                  )                                                  #>                  Warning:                  User supplied limits don't correspond to valid breaks. [0.01, 0.028] rounded to [0.01, 0.03]                                                                                                    # Or extend it.                                                  v                  +                  geom_contour_fill                  (                  aes                  (fill                  =                  stat                  (                  level                  )                  )                  )                  +                                                  scale_fill_discretised                  (low                  =                  "#a62100", high                  =                  "#fff394",                                  limits                  =                  c                  (                  0,                  0.07                  )                  )                                                                                                                    v                  +                  geom_contour_fill                  (                  aes                  (fill                  =                  stat                  (                  level                  )                  )                  )                  +                                                  scale_fill_divergent_discretised                  (midpoint                  =                  0.02                  )                                                                                                                    # Existing continous scales can be "retrofitted" by changing the `super`                                                  # and `guide` arguments.                                                  v                  +                  geom_contour_fill                  (                  aes                  (fill                  =                  stat                  (                  level                  )                  )                  )                  +                                                  scale_fill_distiller                  (super                  =                  ScaleDiscretised                  )                                                                                                                    # Unequal breaks will, by default, map to unequal spacing in the guide                                                  v                  +                  geom_contour_fill                  (                  aes                  (fill                  =                  stat                  (                  level                  )                  ), breaks                  =                  c                  (                  0,                  0.005,                  0.01,                  0.02,                  0.04                  )                  )                  +                                                  scale_fill_discretised                  (                  )                                                                                                                    # You can change that by the `even.steps` argument on ggplot2::guide_colorsteps()                                                  v                  +                  geom_contour_fill                  (                  aes                  (fill                  =                  stat                  (                  level                  )                  ), breaks                  =                  c                  (                  0,                  0.005,                  0.01,                  0.02,                  0.04                  )                  )                  +                                                  scale_fill_discretised                  (guide                  =                  guide_colorsteps                  (even.steps                  =                  TRUE, show.limits                  =                  TRUE                  )                  )