Ordered factors

• Ordered factors, created with ordered(), imply a strict ordering and equal distance between levels:

ordered(c('a', 'b', 'c'))

## [1] a b c
## Levels: a < b < c

• If you map an ordered factor to color or fill in ggplot2, it will default to scale_color_viridis() or scale_fill_viridis().
• If you use an ordered function in a linear model, it will use ‘polygonal contrasts’. These are mildly useful and you can learn more here: vignette("contrasts", package = "faux") by Lisa DeBruine.