r - ggplot : "size-robust" way to place horizontal legend at the bottom-right

Question

我试图在绘图区域外的右下角放置一个水平图例。
我意识到之前已经讨论过这个问题。然而，在一个漫长而令人沮丧的早晨之后，我无法找到一个“大小稳健”的解决方案。
以下是我找到的 3 个解决方案:

当我设置 legend.position至 bottom : 图例位于
底部中心，但我无法使用legend.justification

当我设置 legend.position至 c(1,0) :图例位于
右下角。但是，图例位于情节内。

当我添加 plot.margin并推送 legend.position再向下:
图例位于图的右下角和外部。但是，当我更改绘图区域的大小时，图例不再正确定位。

第三个解决方案定位不正确:


可重现代码:

# Generate random data------

sample.n = 50
sample.data = data.frame(x = runif(sample.n,0,1), y = runif(sample.n,0,1), value = runif(sample.n,0,10))

# Plot ------

library(ggplot2)

# Margins are fine. And If I change the size of the plotting area, the legend will always be bottom- centered
# Problem: Can't push it to the right side  
ggplot(sample.data, aes(x = x, y = y, color = value)) + geom_point() + 
  theme(legend.direction = "horizontal", legend.position = "bottom") 

# Pushed to the bottom-right Successfully 
# Problem: Legend inside the plot
ggplot(sample.data, aes(x = x, y = y, color = value)) + geom_point() + 
  theme(legend.direction = "horizontal",legend.position = c(1,0)) # Problem: inside plot 

# Placed at the bottom-right corner outside the plot region 
# Problem: If I change the size of the plotting region, the legend will not be cornred
ggplot(sample.data, aes(x = x, y = y, color = value)) + geom_point() + 
  theme(legend.direction = "horizontal", legend.position = c(0.9,-0.2),  
        plot.margin = unit(c(1, 1, 5, 1), "lines"))  

主题传奇的文档:

legend.position the position of legends ("none", "left", "right", "bottom", "top", or two-element numeric vector)

legend.justification anchor point for positioning legend inside plot ("center" or two-element numeric vector)

Answer 1

编辑 使用 2.2.0，可以使用 legend.justification 将图例推到右侧和 legend.margin在主题中。

# Generate random data------

sample.n = 50
sample.data = data.frame(x = runif(sample.n,0,1), y = runif(sample.n,0,1), value = runif(sample.n,0,10))

# Plot ------

library(ggplot2)
library(gtable)
library(grid)

p = ggplot(sample.data, aes(x = x, y = y, color = value)) + geom_point() + 
  theme(legend.direction = "horizontal", legend.position = "bottom",
          legend.box.background = element_rect(colour = "black"))

p + theme(legend.justification = "right",
          legend.margin = margin(t = 2, r = 0, b = 2, l = 2, unit = "mm"))

对于它的值(value)，我保留了原始答案，但已更新为 ggplot 2.2.0 版。

我在这里所做的是从图中提取图例，将图例包装在视口(viewport)中，使视口(viewport)位于右侧，将图例放回图中，并删除原始图例。

# Generate random data------

sample.n = 50
sample.data = data.frame(x = runif(sample.n,0,1), y = runif(sample.n,0,1), value = runif(sample.n,0,10))

# Plot ------

library(ggplot2)
library(gtable)
library(grid)

p = ggplot(sample.data, aes(x = x, y = y, color = value)) + geom_point() + 
  theme(legend.direction = "horizontal", legend.position = "bottom")

# Get the ggplot grob
g = ggplotGrob(p)

# Get the legend
index = which(g$layout$name == "guide-box")
leg = g$grobs[[index]]

# Wrap the legend in a viewport
leg$vp = viewport(x = unit(1, "npc"), width = sum(leg$widths), just = "right")

### Put the legend back into the plot
     # First, get the current location of the legend
pos = g$layout[index, ]
g = gtable_add_grob(g, leg, t = pos$t, l = pos$l)

# Remove the original legend
g$grobs <- g$grobs[-index]
g$layout <- g$layout[-index, ]

# Draw the chart
grid.newpage()
grid.draw(g)

请注意，图例已移至右侧，但图例的右边缘与绘图面板的右边缘并不完全对齐。这是因为图例具有内部边距。图例本身有一个边距，但该边距设置为 0 毫米。要使图例与绘图面板对齐，需要更多的摆弄。在接下来的内容中，内部边距(和图例边距)设置为 0。此外，图例和图例的内部部分被包裹在右对齐的视口(viewport)中。

# Get the ggplot grob
g = ggplotGrob(p)

# Get the legend
index = which(g$layout$name == "guide-box")
leg = g$grobs[[index]]

# Remove the legend right margin and an internal margin
leg$widths[4] = unit(0, "mm")
leg$grobs[[1]]$widths[5] = unit(0, "mm")

# Wrap the legend in a viewport
leg$vp = viewport(x = unit(1, "npc"), width = sum(leg$widths), just = "right")

# Wrap the internal part of the legend in a right justified viewport
leg$grobs[[1]]$vp = viewport(x = unit(1, "npc"), width = sum(leg$grobs[[1]]$widths), just = "right")

### Put the legend back into the plot
     # First, get the current location of the legend
pos = g$layout[index, ]
g = gtable_add_grob(g, leg, t = pos$t, l = pos$l)

# Remove the original legend
g$grobs <- g$grobs[-index]
g$layout <- g$layout[-index, ]

# Draw the chart
grid.newpage()
grid.draw(g)