Cycle a bounded set of colour indices over the values of a key

The order-stable primitive behind [assign_cycle_colours()] (and so [radiate()]'s `colour_cycle`). Maps each value of `x` to an index in `1:n`, numbering the distinct values by `levels` and wrapping back to `1` after every `n`. Passing an explicit `levels` lets two data frames that share a key (for example tracks and an overlay drawn on top of them) be coloured identically, so a given key value gets the same colour in both.

Usage

cycle_colours(x, n, levels = NULL)

Arguments

x

A vector of key values (e.g. trajectory ids or a grouping column).

n

Number of colours to cycle through (a positive integer).

levels

Optional ordering of the distinct key values. Defaults to their order of first appearance in `x`. Supply a shared ordering to colour two frames consistently.

Value

A factor the same length as `x` with levels `"1"`..`"n"` giving the cycled colour index. `NA` in `x` is preserved as `NA`.

See also

[assign_cycle_colours()], [radiate()]

Examples

cycle_colours(c("a", "b", "c", "a"), n = 2)
#> [1] 1 2 1 1
#> Levels: 1 2