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Provides sequential colour scales from Paul Tol's Colour Schemes.

Arguments

...

Arguments passed to ggplot2::continuous_scale().

reverse

A logical scalar. Should the resulting vector of colors be reversed?

range

A length-two numeric vector specifying the fraction of the scheme's colour domain to keep.

aesthetics

A character string or vector of character strings listing the name(s) of the aesthetic(s) that this scale works with.

discrete

A logical scalar: should the colour scheme be used as a discrete scale? If TRUE, it is a departure from Paul Tol's recommendations and likely a very poor use of colour.

Value

A continuous scale.

Details

#'

PaletteMax. colorsNA value
YlOrBr9#888888
iridescent23#999999
discreterainbow23#777777
smoothrainbow34#666666

Interpolation

If more colors than defined are needed from a given scheme, the colour coordinates are linearly interpolated to provide a continuous version of the scheme, with the exception of the discrete rainbow scheme (see below).

Note that the default colour for NA can be overridden by passing a value to ggplot2::continuous_scale().

Rainbow colour scheme

As a general rule, ordered data should not be represented using a rainbow scheme. There are three main arguments against such use (Tol 2018):

  • The spectral order of visible light carries no inherent magnitude message.

  • Some bands of almost constant hue with sharp transitions between them, can be perceived as jumps in the data.

  • Colour-blind people have difficulty distinguishing some colours of the rainbow.

If such use cannot be avoided, Paul Tol's technical note provides two colour schemes that are reasonably clear in colour-blind vision. To remain colour-blind safe, these two schemes must comply with the following conditions:

discreterainbow

This scheme must not be interpolated.

smoothrainbow

This scheme does not have to be used over the full range.

References

Tol, P. (2018). Colour Schemes. SRON. Technical Note No. SRON/EPS/TN/09-002, issue 3.1. URL: https://personal.sron.nl/~pault/data/colourschemes.pdf

Author

N. Frerebeau

Examples

data(faithfuld, package = "ggplot2")

ggplot2::ggplot(faithfuld, ggplot2::aes(waiting, eruptions, fill = density)) +
  ggplot2::geom_raster() +
  scale_fill_YlOrBr()


ggplot2::ggplot(faithfuld, ggplot2::aes(waiting, eruptions, fill = density)) +
  ggplot2::geom_raster() +
  scale_fill_iridescent(reverse = TRUE)


ggplot2::ggplot(faithfuld, ggplot2::aes(waiting, eruptions, fill = density)) +
  ggplot2::geom_raster() +
  scale_fill_smoothrainbow(range = c(0.25, 1))