如何让ggplot2中的图例与我的情节高度相同？

Question

我使用ggplot2（版本0.9.3.1）在R（版本R版本3.0.1（2013-05-16））中生成了一个简单的图，显示了一组数据的相关系数。目前，图表右侧的图例颜色条是整个图块大小的一部分。

我希望图例颜色条与图的高度相同。我以为我可以使用legend.key.height来做这件事，但我发现事实并非如此。我调查了grid包unit函数，发现那里有一些规范化的单位，但是当我尝试它们时（unit(1, "npc")），颜色条太高了，离开了页面。

如何使图例与图块本身的高度相同？

完整的自包含示例如下：

# Load the needed libraries
library(ggplot2)
library(grid)
library(scales)
library(reshape2)

# Generate a collection of sample data
variables = c("Var1", "Var2", "Var3")
data = matrix(runif(9, -1, 1), 3, 3)
diag(data) = 1
colnames(data) = variables
rownames(data) = variables

# Generate the plot
corrs = data
ggplot(melt(corrs), aes(x = Var1, y = Var2, fill = value)) +
  geom_tile() +
  geom_text(parse = TRUE, aes(label = sprintf("%.2f", value)), size = 3, color = "white") +
  theme_bw() +
  theme(panel.border = element_blank(),
        axis.text.x = element_text(angle = 90, vjust = 0.5, hjust = 1),
        aspect.ratio = 1,
        legend.position = "right",
        legend.key.height = unit(1, "inch")) +
        labs(x = "", y = "", fill = "", title = "Correlation Coefficients") +
        scale_fill_gradient2(limits = c(-1, 1), expand = c(0, 0),
                             low = muted("red"),
                             mid = "black",
                             high = muted("blue"))

Answer 1

修改更新到ggplot v3.0.0

这很麻烦，但基于this answer，并深入研究ggplot grob，可以精确定位图例。

# Load the needed libraries
library(ggplot2)
library(gtable)  # 
library(grid)
library(scales)
library(reshape2)

# Generate a collection of sample data
variables = c("Var1", "Var2", "Var3")
data = matrix(runif(9, -1, 1), 3, 3)
diag(data) = 1
colnames(data) = variables
rownames(data) = variables

# Generate the plot
corrs = data
plot  = ggplot(melt(corrs), aes(x = Var1, y = Var2, fill = value)) + 
   geom_tile() +
   theme_bw() + 
   theme(panel.border = element_blank()) +
   theme(axis.text.x = element_text(angle = 90, vjust = 0.5, hjust = 1)) +
   theme(aspect.ratio = 1) +
   # theme(legend.position = "right", legend.key.height = unit(1, "inch")) +
   labs(x = "", y = "", fill = "", title = "Correlation Coefficients") +
   scale_fill_gradient2(limits = c(-1, 1), breaks = c(-1, -.5, 0, .5, 1), expand = c(0,0), 
      low = muted("red"), mid = "black", high = muted("blue")) +  # Modified line
   geom_text(parse = TRUE, aes(label = sprintf("%.2f", value)), size = 3, color = "white") +
   scale_x_discrete(expand = c(0,0)) +  # New line
   scale_y_discrete(expand = c(0,0))    # New line
plot

# Get the ggplot grob
gt = ggplotGrob(plot)

# Get the legend
leg = gtable_filter(gt, "guide-box")

# Raster height
leg[[1]][[1]][[1]][[1]][[1]][[2]]$height = unit(1, "npc")

# Positions for labels and tick marks - five breaks, therefore, five positions
pos = unit.c(unit(0.01,"npc"), unit(.25, "npc"), unit(.5, "npc"), unit(.75, "npc"), unit(.99, "npc"))

# Positions the labels 
leg[[1]][[1]][[1]][[1]][[1]][[3]]$children[[1]]$y = pos

# Positions the tick marks
leg[[1]][[1]][[1]][[1]][[1]][[5]]$y0 = pos
leg[[1]][[1]][[1]][[1]][[1]][[5]]$y1 = pos

# Legend key height ?
leg[[1]][[1]][[1]][[1]]$heights = unit.c(rep(unit(0, "mm"), 3),
                                         unit(1, "npc"),
                                         unit(0, "mm"))
# Legend height
leg[[1]][[1]]$heights[[3]] = sum(rep(unit(0, "mm"), 3),
                                 unit(1, "npc"),
                                 unit(0, "mm"))

# grid.draw(leg)  # Check on heights and y values

# gtable_show_layout(gt) # Manually locate position of legend in layout
gt.new = gtable_add_grob(gt, leg, t = 7, l = 9)

# Draw it
grid.newpage()
grid.draw(gt.new)

Answer 2

这看起来相当棘手，我得到的最接近的是

## panel height is 1null, so we work it out by subtracting the other heights from 1npc
## and 1line for the default plot margins

panel_height = unit(1,"npc") - sum(ggplotGrob(plot)[["heights"]][-3]) - unit(1,"line")
plot + guides(fill= guide_colorbar(barheight=panel_height))

不幸的是，垂直理由有点偏。