Palettes: what turns a value's place among the data into a value of its aesthetic, a colour, a size, a shape or a line type. A palette is a value naming its function, so it compares and prints. A continuous palette is handed places, 0 to 1 over the data's range (continuous/2); a discrete one the number of levels it must tell apart (discrete/2).

Continuous palettes

• :identity, R's pal_identity(): each place as it is.
• {:rescale, {low, high}}, R's pal_rescale(): each place moved onto low to high.
• {:area, {low, high}}, R's pal_area(): each place's square root moved onto low to high, so an area drawn at that size grows with the place.
• {:abs_area, max}, R's abs_area(): the square root of each place's size moved onto 0 to max; a place may lie below 0 or past 1.
• {:gradient, colors}, R's pal_gradient_n(), which R's two- and three-colour gradients are too: the colour that far along a gradient through colors, spaced evenly from 0 to 1, each place between two blended in CIE Lab* and its alpha along a straight line; a place at a colour takes it exactly, one outside 0 to 1 gives nil, and one colour is every place's. :none among the colours is R's NA, white with no alpha, as "transparent" is.
• {:gradient, colors, values}, R's pal_gradient_n(colours, values): each place moved first along the straight lines through values, each value at its own place spread evenly from 0 to 1, then taken along the gradient; a place outside the values gives nil. The values are taken as R's approxfun() takes them: sorted, so unsorted ones run the gradient backwards; a nil dropped; equal values one, at their places' mean; as many as you like, not one per colour. Fewer than two left raise ArgumentError. R also warns of equal values.

Discrete palettes

• {:hue, %{hue: {low, high}, chroma: chroma, luminance: luminance, direction: direction}}, R's pal_hue(): colours of one chroma and luminance, their hues spaced evenly from low to high, handed out in reverse for a direction of -1. A range within a degree of the whole circle leaves its last share off, since its end is its start.
• {:gray, {start, finish}}, R's pal_grey(): greys from the level start to finish, 0 black and 1 white, spaced evenly once raised to the power 2.2.
• {:viridis, %{option: option, begin: begin, end: end, direction: direction, alpha: alpha}}, R's pal_viridis(): colours of a viridis palette, as Scales.ColorOperations.viridis/2 gives them.
• {:shape, :solid} or {:shape, :open}, R's pal_shape(): six shapes by name, solid (:circle_small, :triangle, :square, :plus, :square_cross, :asterisk, R's 16, 17, 15, 3, 7 and 8) or open (:circle_open, :triangle_open, :square_open and the same last three, R's 1, 2, 0, 3, 7 and 8).
• :linetype, R's pal_linetype(): 13 line types, each as its dash pattern, a tuple of lengths, {} for a solid line.
• {:manual, values}, R's pal_manual(): values in order.
• {:brewer, %{palette: palette, direction: direction}}, R's pal_brewer(): the colours of one of ColorBrewer's palettes, named as R spells it (brewer_palettes/1 lists them), which has a set of its own for each count from 3 to its largest. Fewer than 3 levels take the start of its set of 3, and a direction of -1 hands the colours out in reverse once the nils past its largest set are added, so those come first, as R's do. A name it does not know is refused, where R warns and gives Greens.

A discrete palette asked for more levels than it holds gives nil for each past its end, as R gives NA (and warns). No levels give none, where R's hue palette refuses them.

A palette of the other kind

Each function takes a palette of the other kind too, as R's as_continuous_pal() and as_discrete_pal() convert one. continuous/2 hands a discrete palette of colours on as a gradient through its nlevels/1 colours, and one of numbers as those numbers joined by straight lines, spaced evenly from 0 to 1; a place outside them gives nil, and a palette of shapes, line types or other values is refused. discrete/2 hands a continuous palette the levels' places, spaced evenly from 0 to 1 by spread/2. :identity and {:abs_area, max}, which R gives no type, are not converted: R hands them back as they are, so asked for 3 levels they give the one number 3, and here they are refused.

Colours are uppercase #RRGGBB, or #RRGGBBAA with an alpha of their own, as Scales.ColorOperations writes them.

ColorBrewer

This product includes color specifications and designs developed by Cynthia Brewer (http://colorbrewer.org/). They are Copyright (c) 2002 Cynthia Brewer, Mark Harrower, and The Pennsylvania State University, licensed under the Apache License, Version 2.0, as R's RColorBrewer carries them.