openColours: openair colours
In davidcarslaw/ggopenair: Tools for the Analysis of Air Pollution Data

Description Usage Arguments Details Value Author(s) References Examples

Pre-defined openair colours and definition of user-defined colours

1	openColours(scheme = "default", n = 100)

scheme

The pre-defined schemes are "increment", "default", "brewer1", "heat", "jet", "hue", "greyscale", or a vector of R colour names e.g. c("green", "blue"). It is also possible to supply colour schemes from the RColorBrewer package. This package defines three types of colour schemes: sequential, diverging or qualitative. See http://colorbrewer2.org for more details concerning the orginal work on which this is based.

Sequential colours are useful for ordered data where there is a need to show a difference between low and high values with colours going from light to dark. The pre-defined colours that can be supplied are: "Blues", "BuGn", "BuPu", "GnBu", "Greens", "Greys", "Oranges", "OrRd", "PuBu", "PuBuGn", "PuRd", "Purples", "RdPu", "Reds", "YlGn", "YlGnBu", "YlOrBr", "YlOrRd".

Diverging palettes put equal emphasis on mid-range critical values and extremes at both ends of the data range. Pre-defined values are: "BrBG", "PiYG", "PRGn", "PuOr", "RdBu", "RdGy", "RdYlBu", "RdYlGn", "Spectral".

Qualitative palettes are useful for differentiating between categorical data types. The pre-defined schemes are "Accent", "Dark2", "Paired", "Pastel1", "Pastel2", "Set1", "Set2", "Set3".

Note that because of the way these schemes have been developed they only exist over certain number of colour gradations (typically 3–10) — see ?brewer.pal for actual details. If less than or more than the required number of colours is supplied then openair will interpolate the colours.

n

number of colours required.

This in primarily an internal openair function to make it easy for users to select particular colour schemes, or define their own range of colours of a user-defined length.

Each of the pre-defined schemes have merits and their use will depend on a particular situation. For showing incrementing concentrations e.g. high concentrations emphasised, then "default", "heat", "jet" and "increment" are very useful. See also the description of RColorBrewer schemes for the option scheme.

To colour-code categorical-type problems e.g. colours for different pollutants, "hue" and "brewer1" are useful.

When publishing in black and white, "greyscale" is often convenient. With most openair functions, as well as generating a greyscale colour gradient, it also resets strip background and other coloured text and lines to greyscale values.

Failing that, the user can define their own schemes based on R colour names. To see the full list of names, type colors() into R.

Returns colour values - see examples below.

David Carslaw

http://colorbrewer2.org

# to return 5 colours from the "jet" scheme:
cols <- openColours("jet", 5)
cols

# to interpolate between named colours e.g. 10 colours from yellow to
#  green to red:
cols <- openColours(c("yellow", "green", "red"), 10)
cols