I’m very pleased to announce the release of ggplot2 2.0.0. I know I promised that there wouldn’t be any more updates, but while working on the 2nd edition of the ggplot2 book, I just couldn’t stop myself from fixing some long standing problems. On the scale of ggplot2 releases, this one is huge with over one hundred fixes and improvements. This might break some of your existing code (although I’ve tried to minimise breakage as much as possible), but I hope the new features make up for any short term hassle. This blog post documents the most important changes:
- ggplot2 now has an official extension mechanism.
- There are a handful of new geoms, and updates to existing geoms.
- The default appearance has been thoroughly tweaked so most plots should look better.
- Facets have a much richer set of labelling options.
- The documentation has been overhauled to be more helpful, and require less integration across multiple pages.
- A number of older and less used features have been deprecated.
ExtensibilityPerhaps the bigggest news in this release is that ggplot2 now has an official extension mechanism. This means that others can now easily create their on stats, geoms and positions, and provide them in other packages. This should allow the ggplot2 community to flourish, even as less development work happens in ggplot2 itself. See
vignette("extending-ggplot2")for details. Coupled with this change, ggplot2 no longer uses proto or reference classes. Instead, we now use ggproto, a new OO system designed specifically for ggplot2. Unlike proto and RC, ggproto supports clean cross-package inheritance, which is necessary for extensibility. Creating a new OO system isn’t usually the right solution, but I’m pretty sure it was necessary here. Read more about it in the vignette.
New and updated geoms
- ggplot no longer throws an error if you your plot has no layers. Instead it automatically adds
ggplot(mpg, aes(cyl, hwy))
geom_count()(a new alias for the old
stat_sum()) counts the number of points at unique locations on a scatterplot, and maps the size of the point to the count:
ggplot(mpg, aes(cty, hwy)) + geom_point() ggplot(mpg, aes(cty, hwy)) + geom_count()
geom_curve()draws curved lines in the same way that
geom_segment()draws straight lines:
df <- expand.grid(x = 1:2, y = 1:2) ggplot(df, aes(x, y, xend = x + 0.5, yend = y + 0.5)) + geom_curve(aes(colour = "curve")) + geom_segment(aes(colour = "segment"))
geom_bar()now behaves differently from
geom_histogram(). Instead of binning the data, it counts the number of unique observations at each location:
ggplot(mpg, aes(cyl)) + geom_bar() ggplot(mpg, aes(cyl)) + geom_histogram(binwidth = 1)If you got into the (bad) habit of using
geom_histogram()to create bar charts, or
geom_bar()to create histograms, you’ll need to switch.
- Layers are now much stricter about their arguments – you will get an error if you’ve supplied an argument that isn’t an aesthetic or a parameter. This breaks the handful of geoms/stats that used
...to pass additional arguments on to the underlying computation. Now
fun.args. This is likely to cause some short-term pain but in the long-term it will make it much easier to spot spelling mistakes and other errors.
geom_text()has been overhauled to make labelling your data a little easier. You can use
nudge_yarguments to offset labels from their corresponding points.
check_overlap = TRUEprovides a simple way to avoid overplotting of labels: labels that would otherwise overlap are omitted.
ggplot(mtcars, aes(wt, mpg, label = rownames(mtcars))) + geom_point() + geom_text(nudge_y = 0.5, check_overlap = TRUE)(Labelling points well is still a huge pain, but at least these new features make life a lit better.)
geom_text()but draws a rounded rectangle underneath each label:
grid <- expand.grid( x = seq(-pi, pi, length = 50), y = seq(-pi, pi, length = 50) ) %>% mutate(r = x ^ 2 + y ^ 2, z = cos(r ^ 2) * exp(-r / 6)) ggplot(grid, aes(x, y)) + geom_raster(aes(fill = z)) + geom_label(data = data.frame(x = 0, y = 0), label = "Center") + theme(legend.position = "none") + coord_fixed()
aes_q(), and works like the SE functions in dplyr and my other recent packages. It supports formulas, so the most concise SE version of
aes(carat, price)is now
aes_(~carat, ~price). You may want to use this form in packages, as it will avoid spurious
R CMD checkwarnings about undefined global variables.
ggplot(mpg, aes_(~displ, ~cty)) + geom_point() # Same as ggplot(mpg, aes(displ, cty)) + geom_point()
AppearanceI’ve made a number of small tweaks to the default appearance:
- The default
theme_grey()background colour has been changed from “grey90” to “grey92”: this makes the background a little less visually prominent.
- Labels and titles have been tweaked for readability. Axis labels are darker, and legend titles get the same visual treatment as axis labels.
- The default font size dropped from 12 to 11. You might be surprised that I’ve made the default text size smaller as it was already hard for many people to read. It turns out there was a bug in RStudio (fixed in 0.99.724), that shrunk the text of all grid based graphics. Once that was resolved the defaults seemed too big to my eyes.
scale_size()now maps values to area, not radius. Use
scale_radius()if you want the old behaviour (not recommended, except perhaps for lines). Continue to use
scale_size_area()if you want 0 values to have 0 area.
- Bar and rectangle legends no longer get a diagonal line. Instead, the border has been tweaked to make it visible, and more closely match the size of line drawn on the plot.
ggplot(mpg, aes(factor(cyl), fill = drv)) + geom_bar(colour = "black", size = 1) + coord_flip()
geom_point()now uses shape 19 instead of 16. This looks much better on the default Linux graphics device. (It’s very slightly smaller than the old point, but it shouldn’t affect any graphics significantly). You can now control the width of the outline on shapes 21-25 with the
- The default legend will now allocate multiple rows (if vertical) or columns (if horizontal) in order to make a legend that is more likely to fit on the screen. You can override with the
p <- ggplot(mpg, aes(displ,hwy, colour = manufacturer)) + geom_point() + theme(legend.position = "bottom") p # Revert back to previous behaviour p + guides(colour = guide_legend(nrow = 1))
- Two new themes were contributed by Jean-Olivier Irisson:
theme_void()is completely empty and
theme_dark()has a dark background designed to make colours pop out.
Facet labelsThanks to the work of Lionel Henry, facet labels have received three major improvements:
- You can switch the position of facet labels so they’re next to the axes.
facet_wrap()now supports custom labellers.
- You can create combined labels when facetting by multiple variables.
Switching the labelsThe new
switchargument allows you to switch the labels to display near the axes:
data <- transform(mtcars, am = factor(am, levels = 0:1, c("Automatic", "Manual")), gear = factor(gear, levels = 3:5, labels = c("Three", "Four", "Five")) ) ggplot(data, aes(mpg, disp)) + geom_point() + facet_grid(am ~ gear, switch = "both")This is especially useful when the labels directly characterise the axes. In that situation, switching the labels can make the plot clearer and more readable. You may also want to use a neutral label background by setting
data <- mtcars %>% mutate( Logarithmic = log(mpg), Inverse = 1 / mpg, Cubic = mpg ^ 3, Original = mpg ) %>% tidyr::gather(transformation, mpg2, Logarithmic:Original) ggplot(data, aes(mpg2, disp)) + geom_point() + facet_wrap(~transformation, scales = "free", switch = "x") + theme(strip.background = element_blank())
Wrap labellerA longstanding issue in ggplot was that
facet_wrap()did not support custom labellers. Labellers are small functions that make it easy to customise the labels. You can now supply labellers to both wrap and grid facets:
ggplot(data, aes(mpg2, disp)) + geom_point() + facet_wrap(~transformation, scales = "free", labeller = "label_both")
Composite marginsLabellers have now better support for composite margins when you facet over multiple variable with
+. All labellers gain a
multi_lineargument to control whether labels should be displayed as a single line or over multiple lines, one for each factor. The labellers still work the same way except for
label_bquote(). That labeller makes it easy to write mathematical expression involving the values of facetted factors. Historically,
label_bquote()could only specify a single expression for all margins and factor. The factor value was referred to via the backquoted placeholder
.(x). Now that it supports expressions combining multiple factors, you must backquote the variable names themselves. In addition, you can provide different expressions for each margin:
my_labeller <- label_bquote( rows = .(am) / alpha, cols = .(vs) ^ .(cyl) ) ggplot(mtcars, aes(wt, mpg)) + geom_point() + facet_grid(am ~ vs + cyl, labeller = my_labeller)
DocumentationI’ve given the documentation a thorough overhaul:
- Tighly linked geoms and stats (e.g.
stat_boxplot()) are now documented in the same file so you can see all the arguments in one place. Similarly, variations on a theme (like
geom_step()) are documented together.
- I’ve tried to reduce the use of
...so that you can see all the documentation in one place rather than having to follow links around. In some cases this has involved adding additional arguments to geoms to make it more clear what you can do.
- Thanks to Bob Rudis, the use of
qplot()in examples has been grealy reduced. This is inline with the 2nd edition of the ggplot2 book, which eliminates
qplot()in favour of
orderaesthetic is officially deprecated. It never really worked, and was poorly documented.
qplot()have been deprecated.
qplot()is designed for quick plots – if you need to specify position or stat, use
- The theme setting
axis.ticks.marginhas been deprecated: now use the margin property of
stat_vline()have been removed: these were never suitable for use other than with their corresponding geoms and were not documented.
show_guidehas been renamed to
show.legend: this more accurately reflects what it does (controls appearance of layer in legend), and uses the same convention as other ggplot2 arguments (i.e. a
.between names). (Yes, I know that’s inconsistent with function names (which use
_) but it’s too late to change now.)
stat_bin2d()have been renamed to
stat_summary2d()has been renamed to
stat_density2d()has been renamed to
geom_spoke()since I realised it’s a reparameterisation of
stat_bindot()has been removed because it’s so tightly coupled to
geom_dotplot(). If you happened to use
stat_bindot(), just change to