I’m very pleased to announce ggplot2 2.2.0. It includes four major new features:

• Subtitles and captions.
• A large rewrite of the facetting system.
• Improved theme options.
• Better stacking.

It also includes as numerous bug fixes and minor improvements, as described in the release notes.

The majority of this work was carried out by Thomas Pederson, who I was lucky to have as my “ggplot2 intern” this summer. Make sure to check out his other visualisation packages: ggraph, ggforce, and tweenr.

Install ggplot2 with:

install.packages("ggplot2")

Subtitles and captions

Thanks to Bob Rudis, you can now add subtitles and captions to your plots:

ggplot(mpg, aes(displ, hwy)) +
  geom_point(aes(color = class)) +
  geom_smooth(se = FALSE, method = "loess") +
  labs(
    title = "Fuel efficiency generally decreases with engine size",
    subtitle = "Two seaters (sports cars) are an exception because of their light weight",
    caption = "Data from fueleconomy.gov"
  )

These are controlled by the theme settings plot.subtitle and plot.caption.

The plot title is now aligned to the left by default. To return to the previous centered alignment, use theme(plot.title = element_text(hjust = 0.5)).

Facets

The facet and layout implementation has been moved to ggproto and received a large rewrite and refactoring. This will allow others to create their own facetting systems, as descrbied in the vignette("extending-ggplot2"). Along with the rewrite a number of features and improvements has been added, most notably:

• ou can now use functions in facetting formulas, thanks to Dan Ruderman.

  ggplot(diamonds, aes(carat, price)) + 
    geom_hex(bins = 20) + 
    facet_wrap(~cut_number(depth, 6))

  

• Axes are now drawn under the panels in facet_wrap() when the rentangle is not completely filled.

  ggplot(mpg, aes(displ, hwy)) + 
    geom_point() + 
    facet_wrap(~class)

  

• You can set the position of the axes with the position argument.

  ggplot(mpg, aes(displ, hwy)) + 
    geom_point() + 
    scale_x_continuous(position = "top") + 
    scale_y_continuous(position = "right")

  

• You can display a secondary axis that is a one-to-one transformation of the primary axis with sec.axis.

  ggplot(mpg, aes(displ, hwy)) + 
    geom_point() + 
    scale_y_continuous(
      "mpg (US)", 
      sec.axis = sec_axis(~ . * 1.20, name = "mpg (UK)")
    )

  

• Strips can be placed on any side, and the placement with respect to axes can be controlled with the strip.placement theme option.

  ggplot(mpg, aes(displ, hwy)) + 
    geom_point() + 
    facet_wrap(~ drv, strip.position = "bottom") + 
    theme(
      strip.placement = "outside",
      strip.background = element_blank(),
      strip.text = element_text(face = "bold")
    ) +
    xlab(NULL)

  

Theming

• The theme() function now has named arguments so autocomplete and documentation suggestions are vastly improved.

• Blank elements can now be overridden again so you get the expected behavior when setting e.g. axis.line.x.

• element_line() gets an arrow argument that lets you put arrows on axes.

  arrow <- arrow(length = unit(0.4, "cm"), type = "closed")
  
  ggplot(mpg, aes(displ, hwy)) + 
    geom_point() + 
    theme_minimal() + 
    theme(
      axis.line = element_line(arrow = arrow)
    )

  

• Control of legend styling has been improved. The whole legend area can be aligned with the plot area and a box can be drawn around all legends:

  ggplot(mpg, aes(displ, hwy, shape = drv, colour = fl)) + 
    geom_point() + 
    theme(
      legend.justification = "top", 
      legend.box = "horizontal",
      legend.box.margin = margin(3, 3, 3, 3, "mm"), 
      legend.margin = margin(),
      legend.box.background = element_rect(colour = "grey50")
    )

  

• panel.margin and legend.margin have been renamed to panel.spacing and legend.spacing respectively, as this better indicates their roles. A new legend.margin actually controls the margin around each legend.

• When computing the height of titles, ggplot2 now inclues the height of the descenders (i.e. the bits g and y that hang underneath). This improves the margins around titles, particularly the y axis label. I have also very slightly increased the inner margins of axis titles, and removed the outer margins.

• The default themes has been tweaked by Jean-Olivier Irisson making them better match theme_grey().

Stacking bars

position_stack() and position_fill() now stack values in the reverse order of the grouping, which makes the default stack order match the legend.

avg_price <- diamonds %>% 
  group_by(cut, color) %>% 
  summarise(price = mean(price)) %>% 
  ungroup() %>% 
  mutate(price_rel = price - mean(price))

ggplot(avg_price) + 
  geom_col(aes(x = cut, y = price, fill = color))

(Note also the new geom_col() which is short-hand for geom_bar(stat = "identity"), contributed by Bob Rudis.)

If you want to stack in the opposite order, try forcats::fct_rev():

ggplot(avg_price) + 
  geom_col(aes(x = cut, y = price, fill = fct_rev(color)))

Additionally, you can now stack negative values:

ggplot(avg_price) + 
  geom_col(aes(x = cut, y = price_rel, fill = color))

The overall ordering cannot necessarily be matched in the presence of negative values, but the ordering on either side of the x-axis will match.

Labels can also be stacked, but the default position is suboptimal:

series <- data.frame(
  time = c(rep(1, 4),rep(2, 4), rep(3, 4), rep(4, 4)),
  type = rep(c('a', 'b', 'c', 'd'), 4),
  value = rpois(16, 10)
)

ggplot(series, aes(time, value, group = type)) +
  geom_area(aes(fill = type)) +
  geom_text(aes(label = type), position = "stack")

You can improve the position with the vjust parameter. A vjust of 0.5 will center the labels inside the corresponding area:

ggplot(series, aes(time, value, group = type)) +
  geom_area(aes(fill = type)) +
  geom_text(aes(label = type), position = position_stack(vjust = 0.5))