为 geom_text 图层显示单独的图例？

Question

我有以下情节：

library(ggplot2)

ib<- data.frame(
  category =   factor(c("Cat1","Cat2","Cat1", "Cat1", "Cat2","Cat1","Cat1", "Cat2","Cat2")),
  city =       c("CITY1","CITY1","CITY2","CITY3", "CITY3","CITY4","CITY5", "CITY6","CITY7"),
  median =     c(1.3560, 2.4830, 0.7230, 0.8100, 3.1480, 1.9640, 0.6185, 1.2205, 2.4000),
  samplesize = c(851, 1794,   47,  189,  185,    9,   94,   16,   65)
  )


p<-ggplot(data=ib, aes(x=city, y=category, size=median, colour=category, label=samplesize)) +
  geom_point(alpha=.6) +
  scale_area(range=c(1,15)) +
  scale_colour_hue(guide="none") +
  geom_text(aes(size = 1), colour="black")
p

（我正在绘制与中值成正比的圆圈，并用代表样本大小的文本标签覆盖。图片位于http://imgur.com/T82cF）

有什么办法可以分开这两个传说吗？我想要一个图例（标记为“中位数”）给出圆圈的比例，另一个图例带有一个我可以标记为“样本大小”的单个字母“a”（甚至更好的数字）。由于这两个属性没有任何关系，将它们捆绑在同一个图例中是没有意义的。

我尝试了各种组合，但我能想到的最好的方法是完全丢失文本图例:)

谢谢你的回答！

Answer 1

更新 scale_area已弃用；scale_size代替使用。该gtable函数gtable_filter()用于提取图例。并修改了代码，用于替换图例之一中的默认图例键。

如果您仍在寻找问题的答案，这里似乎可以满足您的大部分要求，尽管它在某些地方有点麻烦。图例中的符号可以使用kohske 的评论进行更改

困难在于尝试应用两种不同大小的映射。因此，我将点尺寸映射保留在美学声明中，但从美学声明中删除了标签尺寸映射。这意味着必须根据样本大小（fsamplesize）的因子版本的离散值来设置标签大小。生成的图表几乎是正确的，只是未绘制标签大小（即样本大小）的图例。为了解决这个问题，我绘制了一个图表，其中包含根据样本大小的因子版本（但忽略点大小映射）的标签大小映射，以便提取其图例，然后将其插入回第一个图表中。

## Your data
ib<- data.frame(
  category =   factor(c("Cat1","Cat2","Cat1", "Cat1", "Cat2","Cat1","Cat1", "Cat2","Cat2")),
  city =       c("CITY1","CITY1","CITY2","CITY3", "CITY3","CITY4","CITY5", "CITY6","CITY7"),
  median =     c(1.3560, 2.4830, 0.7230, 0.8100, 3.1480, 1.9640, 0.6185, 1.2205, 2.4000),
  samplesize = c(851, 1794,   47,  189,  185,    9,   94,   16,   65)
  )

## Load packages
library(ggplot2)
library(gridExtra)
library(gtable)
library(grid)

##  Obtain the factor version of samplesize.   
ib$fsamplesize = cut(ib$samplesize, breaks = c(0, 100, 1000, Inf))

## Obtain plot with dot size mapped to median, the label inside the dot set 
## to samplesize, and the size of the label set to the discrete levels of the factor
## version of samplesize. Here, I've selected three sizes for the labels (3, 6 and 10)
## corresponding to samplesizes of 0-100, 100-1000, >1000. The sizes of the labels are
## set using three call to geom_text - one for each size.

p <- ggplot(data=ib, aes(x=city, y=category)) +
   geom_point(aes(size = median, colour = category), alpha = .6) +
   scale_size("Median", range=c(0, 15)) +
   scale_colour_hue(guide = "none") + theme_bw()

p1 <- p + 
  geom_text(aes(label = ifelse(samplesize > 1000, samplesize, "")), 
         size = 10, color = "black", alpha = 0.6) +
  geom_text(aes(label = ifelse(samplesize < 100, samplesize, "")), 
         size = 3, color = "black", alpha = 0.6) +
  geom_text(aes(label = ifelse(samplesize > 100 & samplesize < 1000, samplesize, "")), 
         size = 6, color = "black", alpha = 0.6)


## Extracxt the legend from p1 using functions from the gridExtra package
g1 = ggplotGrob(p1) 
leg1 = gtable_filter(g1, "guide-box")


## Keep p1 but dump its legend
p1 = p1 + theme(legend.position = "none")


## Get second legend - size of the label.
## Draw a dummy plot, using fsamplesize as a size aesthetic. Note that the label sizes are
## set to 3, 6, and 10,  matching the sizes of the labels in p1. 

dummy.plot = ggplot(data = ib, aes(x = city, y = category, label = samplesize)) +
  geom_point(aes(size = fsamplesize), colour = NA) +
  geom_text(show.legend = FALSE) + theme_bw() +
  guides(size = guide_legend(override.aes = list(colour = "black", shape = utf8ToInt("N")))) +
scale_size_manual("Sample Size", values = c(3, 6, 10),
     breaks = levels(ib$fsamplesize), labels = c("< 100", "100 - 1000", "> 1000"))

## Get the legend from dummy.plot using functions from the gridExtra package
g2 = ggplotGrob(dummy.plot) 
leg2 = gtable_filter(g2, "guide-box")


## Arrange the three components (p1, leg1, leg2) using functions from the gridExtra package
## The two legends are arranged using the inner arrangeGrob function. The resulting
## chart is then arranged with  p1 in the outer arrrangeGrob function.
ib.plot = arrangeGrob(p1, arrangeGrob(leg1, leg2, nrow = 2), ncol = 2, 
      widths = unit(c(9, 2), c("null", "null")))

## Draw the graph
grid.newpage()
grid.draw(ib.plot)