wishlist feature requests

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On this page are listed some wish-lists for ggplot2.

~~using rasterGrob as an alternative to geom_tile for regular colormaps~~ Now implemented in 0.9.0
using a custom grob function that draws a shape with color, fill, size arguments (think Chernoff faces, or TeachingDemos::my.symbols())
horizontal versions of all geoms which are not not x/y symmetric: geom_area, geom_bar, geom_boxplot, geom_crossbar, geom_density, geom_freqpoly, geom_histogram, geom_pointrange, geom_linerange, geom_quantile, geom_ribbon, and geom_smooth.
~~geom_dotplot (Cleveland). The current hack with geom_point just doesn't cut it.~~ First implementation in 0.9.0
using Delaunay or Voronoi tesselations to display 2D colormaps of irregular data (see latticeExtra::panel.levelplot.voronoi; packages deldir, Triangle)
geom_brokenpath that plays the role of type="b" in base graphics (a la gridExtra::barbedGrob). In addition, new stat functions that perform the following tasks: cut a path in equispaced segments, add zero-crossing points to shade positive/negative areas

should themes affect the default colour and fill scales? (e.g. a black and white theme could set the default scales to grey)
allow layers to define their own mapping: instead of a generic scale_colour() that applies to all layers, you could have multiple colour scales (or others) in the same plot, each with its own legend.
~~a new kind of geom limited to the use with annotate(), for grobs that are not meant to be mapped to x, y, size, etc. (examples: image annotation, table annotation, etc.)~~ Now annotation_custom, annotation_raster and annotation_map in 0.9.0.
specification of the panel sizes in absolute units, so as to allow alignment between different plots using grid
Allowing a range to be specified on an axis, as kludged together here and here extended in a way described here. In other words, the range would get passed as a start and end coordinate, and a geom_ would be specified elsewhere to determine whether that axis range gets drawn as a brace, box, line, etc. An extension to the extension would be that if both x and y ranges were specified, to draw the braces on the axis and a box highlighting that area on the plot itself.
Complete horizontal/vertical agnosticism. Anything that can be done on the x-axis can just as easily be done on the y-axis. This would eliminate the need for coord_flip() and the headaches it causes. Some details of what this entails are listed in stats and geoms.

ability to specify independently the limits, tick marks, and labels of each panel
ability to set only 1 limit for a scale, and allow the other to be determined by the training, possibly differently for each facet
ability to automatically spread facets over multiple pages and specify number of facets per page (like lattice module). Eg 32 individual graphs spread over 4 pages if request rows=3 and cols=3 in proportions= 9 + 9 + 9 + 5. Presently can only do this by splitting data and using FOR loop. Easier to use lattice!

stack vertically multiple spectra or time series so as to avoid overlap between individual lines
stats that can operate on the vertical dimension, not just the horizontal one (stat_bin, stat_boxplot, stat_density, stat_quantile, stat_smooth, stat_summary)

more options to change the x and y axis parameters independently (grid lines, tick length, etc.)
option to show ticks as separators between discrete values rather than as marker to the respective value
provide the possibility to add labels to stat_contour lines

facilitate navigation to viewports and use of native units
allow switching off clipping to move graphical elements outside the plotting region

Linked micromaps
mailing list discussion
National Cancer Institute Geographic Information Systems software
Daniel Carr, Anthony Olsen, Jean-Yves Courbois, Suzanne Pierson, D. Andrew Carr, "Linked Micromap Plots: Named and Described", Statistical Computing & Statistical Graphics Newsletter 9 (1) 24-32.

color scale where hue, luminance/lightness, and chroma/intensity can each be mapped separately as aesthetics

position_dynamic
deterministic position_jitter so that two geoms with the same set of starting points get jittered to the same locations (say a point and errorbar, or point and text)
position_beeswarm, discussed on the mailing list
dodging in the vertical direction: mailing list discussion