ggplot2 3.3.0

This is a minor release but does contain a range of substantial new features,
along with the standard bug fixes. The release contains a few visual breaking
changes, along with breaking changes for extension developers due to a shift in
internal representation of the position scales and their axes. No user breaking
changes are included.

This release also adds Dewey Dunnington (@paleolimbot) to the core team.

Breaking changes

There are no user-facing breaking changes, but a change in some internal
representations that extension developers may have relied on, along with a few
breaking visual changes which may cause visual tests in downstream packages to
fail.

• The panel_params field in the Layout now contains a list of list of
  ViewScale objects, describing the trained coordinate system scales, instead
  of the list object used before. Any extensions that use this field will likely
  break, as will unit tests that checks aspects of this.

• element_text() now issues a warning when vectorized arguments are provided,
  as in colour = c("red", "green", "blue"). Such use is discouraged and not
  officially supported (@clauswilke, #3492).

• Changed theme_grey() setting for legend key so that it creates no border
  (NA) rather than drawing a white one. (@annennenne, #3180)

• geom_ribbon() now draws separate lines for the upper and lower intervals if
  colour is mapped. Similarly, geom_area() and geom_density() now draw
  the upper lines only in the same case by default. If you want old-style full
  stroking, use outline.type = "full" (@yutannihilation, #3503 / @thomasp85, #3708).

New features

• The evaluation time of aesthetics can now be controlled to a finer degree.
  after_stat() supersedes the use of stat() and ..var..-notation, and is
  joined by after_scale() to allow for mapping to scaled aesthetic values.
  Remapping of the same aesthetic is now supported with stage(), so you can
  map a data variable to a stat aesthetic, and remap the same aesthetic to
  something else after statistical transformation (@thomasp85, #3534)

• All coord_*() functions with xlim and ylim arguments now accept
  vectors with NA as a placeholder for the minimum or maximum value
  (e.g., ylim = c(0, NA) would zoom the y-axis from 0 to the
  maximum value observed in the data). This mimics the behaviour
  of the limits argument in continuous scale functions
  (@paleolimbot, #2907).

• Allowed reversing of discrete scales by re-writing get_limits()
  (@AnneLyng, #3115)

• All geoms and stats that had a direction (i.e. where the x and y axes had
  different interpretation), can now freely choose their direction, instead of
  relying on coord_flip(). The direction is deduced from the aesthetic
  mapping, but can also be specified directly with the new orientation
  argument (@thomasp85, #3506).

• Position guides can now be customized using the new guide_axis(), which can
  be passed to position scale_*() functions or via guides(). The new axis
  guide (guide_axis()) comes with arguments check.overlap (automatic removal
  of overlapping labels), angle (easy rotation of axis labels), and
  n.dodge (dodge labels into multiple rows/columns) (@paleolimbot, #3322).

• A new scale type has been added, that allows binning of aesthetics at the
  scale level. It has versions for both position and non-position aesthetics and
  comes with two new guides (guide_bins and guide_coloursteps)
  (@thomasp85, #3096)

• scale_x_continuous() and scale_y_continuous() gains an n.breaks argument
  guiding the number of automatic generated breaks (@thomasp85, #3102)

• Added stat_contour_filled() and geom_contour_filled(), which compute
  and draw filled contours of gridded data (@paleolimbot, #3044).
  geom_contour() and stat_contour() now use the isoband package
  to compute contour lines. The complete parameter (which was undocumented
  and has been unused for at least four years) was removed (@paleolimbot, #3044).

• Themes have gained two new parameters, plot.title.position and
  plot.caption.position, that can be used to customize how plot
  title/subtitle and plot caption are positioned relative to the overall plot
  (@clauswilke, #3252).

Extensions

• Geom now gains a setup_params() method in line with the other ggproto
  classes (@thomasp85, #3509)

• The newly added function register_theme_elements() now allows developers
  of extension packages to define their own new theme elements and place them
  into the ggplot2 element tree (@clauswilke, #2540).

Minor improvements and bug fixes

• coord_trans() now draws second axes and accepts xlim, ylim,
  and expand arguments to bring it up to feature parity with
  coord_cartesian(). The xtrans and ytrans arguments that were
  deprecated in version 1.0.1 in favour of x and y
  were removed (@paleolimbot, #2990).

• coord_trans() now calculates breaks using the expanded range
  (previously these were calculated using the unexpanded range,
  which resulted in differences between plots made with coord_trans()
  and those made with coord_cartesian()). The expansion for discrete axes
  in coord_trans() was also updated such that it behaves identically
  to that in coord_cartesian() (@paleolimbot, #3338).

• expand_scale() was deprecated in favour of expansion() for setting
  the expand argument of x and y scales (@paleolimbot).

• geom_abline(), geom_hline(), and geom_vline() now issue
  more informative warnings when supplied with set aesthetics
  (i.e., slope, intercept, yintercept, and/or xintercept)
  and mapped aesthetics (i.e., data and/or mapping).

• Fix a bug in geom_raster() that squeezed the image when it went outside
  scale limits (#3539, @thomasp85)

• geom_sf() now determines the legend type automatically (@microly, #3646).

• geom_sf() now removes rows that can't be plotted due to NA aesthetics
  (#3546, @thomasp85)

• geom_sf() now applies alpha to linestring geometries
  (#3589, @yutannihilation).

• gg_dep() was deprecated (@perezp44, #3382).

• Added function ggplot_add.by() for lists created with by(), allowing such
  lists to be added to ggplot objects (#2734, @Maschette)

• ggplot2 no longer depends on reshape2, which means that it no longer
  (recursively) needs plyr, stringr, or stringi packages.

• Increase the default nbin of guide_colourbar() to place the ticks more
  precisely (#3508, @yutannihilation).

• manual_scale() now matches values with the order of breaks whenever
  values is an unnamed vector. Previously, unnamed values would match with
  the limits of the scale and ignore the order of any breaks provided. Note
  that this may change the appearance of plots that previously relied on the
  unordered behaviour (#2429, @idno0001).

• scale_manual_*(limits = ...) now actually limits the scale (#3262,
  @yutannihilation).

• Fix a bug when show.legend is a named logical vector
  (#3461, @yutannihilation).

• Added weight aesthetic option to stat_density() and made scaling of
  weights the default (@annennenne, #2902)

• stat_density2d() can now take an adjust parameter to scale the default
  bandwidth. (#2860, @haleyjeppson)

• stat_smooth() uses REML by default, if method = "gam" and
  gam's method is not specified (@ikosmidis, #2630).

• stacking text when calculating the labels and the y axis with
  stat_summary() now works (@ikosmidis, #2709)

• stat_summary() and related functions now support rlang-style lambda functions
  (#3568, @dkahle).

• The data mask pronoun, .data, is now stripped from default labels.

• Addition of partial themes to plots has been made more predictable;
  stepwise addition of individual partial themes is now equivalent to
  addition of multple theme elements at once (@clauswilke, #3039).

• Facets now don't fail even when some variable in the spec are not available
  in all layers (@yutannihilation, #2963).