ggplot2 3.2.0

This is a minor release with an emphasis on internal changes to make ggplot2
faster and more consistent. The few interface changes will only affect the
aesthetics of the plot in minor ways, and will only potentially break code of
extension developers if they have relied on internals that have been changed.
This release also sees the addition of Hiroaki Yutani (@yutannihilation) to the
core developer team.

With the release of R 3.6, ggplot2 now requires the R version to be at least 3.2,
as the tidyverse is committed to support 5 major versions of R.

Breaking changes

• Two patches (#2996 and #3050) fixed minor rendering problems. In most cases,
  the visual changes are so subtle that they are difficult to see with the naked
  eye. However, these changes are detected by the vdiffr package, and therefore
  any package developers who use vdiffr to test for visual correctness of ggplot2
  plots will have to regenerate all reference images.

• In some cases, ggplot2 now produces a warning or an error for code that previously
  produced plot output. In all these cases, the previous plot output was accidental,
  and the plotting code uses the ggplot2 API in a way that would lead to undefined
  behavior. Examples include a missing group aesthetic in geom_boxplot() (#3316),
  annotations across multiple facets (#3305), and not using aesthetic mappings when
  drawing ribbons with geom_ribbon() (#3318).

New features

• This release includes a range of internal changes that speeds up plot
  generation. None of the changes are user facing and will not break any code,
  but in general ggplot2 should feel much faster. The changes includes, but are
  not limited to:

  • Caching ascent and descent dimensions of text to avoid recalculating it for
    every title.

  • Using a faster data.frame constructor as well as faster indexing into
    data.frames

  • Removing the plyr dependency, replacing plyr functions with faster
    equivalents.

• geom_polygon() can now draw polygons with holes using the new subgroup
  aesthetic. This functionality requires R 3.6.0 (@thomasp85, #3128)

• Aesthetic mappings now accept functions that return NULL (@yutannihilation,
  #2997).

• stat_function() now accepts rlang/purrr style anonymous functions for the
  fun parameter (@dkahle, #3159).

• geom_rug() gains an "outside" option to allow for moving the rug tassels to
  outside the plot area (@njtierney, #3085) and a length option to allow for
  changing the length of the rug lines (@daniel-wells, #3109).

• All geoms now take a key_glyph paramter that allows users to customize
  how legend keys are drawn (@clauswilke, #3145). In addition, a new key glyph
  timeseries is provided to draw nice legends for time series
  (@mitchelloharawild, #3145).

Extensions

• Layers now have a new member function setup_layer() which is called at the
  very beginning of the plot building process and which has access to the
  original input data and the plot object being built. This function allows the
  creation of custom layers that autogenerate aesthetic mappings based on the
  input data or that filter the input data in some form. For the time being, this
  feature is not exported, but it has enabled the development of a new layer type,
  layer_sf() (see next item). Other special-purpose layer types may be added
  in the future (@clauswilke, #2872).

• A new layer type layer_sf() can auto-detect and auto-map sf geometry
  columns in the data. It should be used by extension developers who are writing
  new sf-based geoms or stats (@clauswilke, #3232).

• x0 and y0 are now recognized positional aesthetics so they will get scaled
  if used in extension geoms and stats (@thomasp85, #3168)

• Continuous scale limits now accept functions which accept the default
  limits and return adjusted limits. This makes it possible to write
  a function that e.g. ensures the limits are always a multiple of 100,
  regardless of the data (@econandrew, #2307).

Minor improvements and bug fixes

• cut_width() now accepts ... to pass further arguments to base::cut.default()
  like cut_number() and cut_interval() already did (@cderv, #3055)

• coord_map() now can have axes on the top and right (@karawoo, #3042).

• coord_polar() now correctly rescales the secondary axis (@linzi-sg, #3278)

• coord_sf(), coord_map(), and coord_polar() now squash -Inf and Inf
  into the min and max of the plot (@yutannihilation, #2972).

• coord_sf() graticule lines are now drawn in the same thickness as panel grid
  lines in coord_cartesian(), and seting panel grid lines to element_blank()
  now also works in coord_sf()
  (@clauswilke, #2991, #2525).

• economics data has been regenerated. This leads to some changes in the
  values of all columns (especially in psavert), but more importantly, strips
  the grouping attributes from economics_long.

• element_line() now fills closed arrows (@yutannihilation, #2924).

• Facet strips on the left side of plots now have clipping turned on, preventing
  text from running out of the strip and borders from looking thicker than for
  other strips (@karawoo, #2772 and #3061).

• ggplot2 now works in Turkish locale (@yutannihilation, #3011).

• Clearer error messages for inappropriate aesthetics (@clairemcwhite, #3060).

• ggplot2 no longer attaches any external packages when using functions that
  depend on packages that are suggested but not imported by ggplot2. The
  affected functions include geom_hex(), stat_binhex(),
  stat_summary_hex(), geom_quantile(), stat_quantile(), and map_data()
  (@clauswilke, #3126).

• geom_area() and geom_ribbon() now sort the data along the x-axis in the
  setup_data() method rather than as part of draw_group() (@thomasp85,
  #3023)

• geom_hline(), geom_vline(), and geom_abline() now throw a warning if the
  user supplies both an xintercept, yintercept, or slope value and a
  mapping (@RichardJActon, #2950).

• geom_rug() now works with coord_flip() (@has2k1, #2987).

• geom_violin() no longer throws an error when quantile lines fall outside
  the violin polygon (@thomasp85, #3254).

• guide_legend() and guide_colorbar() now use appropriate spacing between legend
  key glyphs and legend text even if the legend title is missing (@clauswilke, #2943).

• Default labels are now generated more consistently; e.g., symbols no longer
  get backticks, and long expressions are abbreviated with ...
  (@yutannihilation, #2981).

• All-Inf layers are now ignored for picking the scale (@yutannihilation,
  #3184).

• Diverging Brewer colour palette now use the correct mid-point colour
  (@dariyasydykova, #3072).

• scale_color_continuous() now points to scale_colour_continuous() so that
  it will handle type = "viridis" as the documentation states (@hlendway,
  #3079).

• scale_shape_identity() now works correctly with guide = "legend"
  (@malcolmbarrett, #3029)

• scale_continuous will now draw axis line even if the length of breaks is 0
  (@thomasp85, #3257)

• stat_bin() will now error when the number of bins exceeds 1e6 to avoid
  accidentally freezing the user session (@thomasp85).

• sec_axis() now places ticks accurately when using nonlinear transformations (@dpseidel, #2978).

• facet_wrap() and facet_grid() now automatically remove NULL from facet
  specs, and accept empty specs (@yutannihilation, #3070, #2986).

• stat_bin() now handles data with only one unique value (@yutannihilation
  #3047).

• sec_axis() now accepts functions as well as formulas (@yutannihilation, #3031).

• New theme elements allowing different ticks lengths for each axis. For instance,
  this can be used to have inwards ticks on the x-axis (axis.ticks.length.x) and
  outwards ticks on the y-axis (axis.ticks.length.y) (@pank, #2935).

• The arguments of Stat*$compute_layer() and Position*$compute_layer() are
  now renamed to always match the ones of Stat$compute_layer() and
  Position$compute_layer() (@yutannihilation, #3202).

• geom_*() and stat_*() now accepts purrr-style lambda notation
  (@yutannihilation, #3138).

• geom_tile() and geom_rect() now draw rectangles without notches at the
  corners. The style of the corner can be controlled by linejoin parameters
  (@yutannihilation, #3050).