我怎樣才能讓ggplot2中的圖例與我的情節一樣高？

Question

我使用ggplot2（版本0.9.3.1）在R（版本R版本3.0.1（2013-05-16））中生成了一個簡單圖表，顯示了一組數據的相關係數。目前，繪圖右側的圖例顏色條是整個繪圖尺寸的一小部分。

我希望圖例顏色條與圖的高度相同。我認爲我可以使用legend.key.height來做到這一點，但我發現情況並非如此。我調查了grid程序包unit函數，發現裏面有一些標準化的單元，但是當我嘗試它們時（unit(1, "npc")），顏色條顯得太高而離開了頁面。

我怎樣才能讓圖例與情節本身一樣高呢？

一個完整的自包含的例子如下：

# 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

它似乎很棘手，我得到的最接近的是這樣的，

## 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，垂直理由是有點關閉。

Answer 2

這很混亂，但基於this answer，深入研究ggplot grob，可以精確定位圖例。

# 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]]$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 = 6, l = 8) 

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