如何在一个ggplot中拥有两个不同大小的图例？

想象一下我绘制这个玩具数据：

lev <- c("A", "B", "C", "D")

nodes <- data.frame(ord=c(1,1,1,2,2,3,3,4), brand=
  factor(c("A", "B", "C","B", "C","D", "B","D"), levels=lev), 
  thick=c(16,9,9,16,4,1,4,1))

edge <-  data.frame(ord1=c(1,1,2,3), brand1=factor(c("C","A","B","B"), 
  levels=lev),ord2=c(2,2,3,4), brand2=c("C","B","B","D"),
  N1=c(2,1,2,1), N2=c(5,5,2,1))

ggplot() +
  geom_point(data = nodes,
    aes(x = ord, y = brand, size = sqrt(thick)),
    color = "black", shape = 16, show.legend = T) + 
  scale_x_continuous(limits=c(1, 4), breaks=seq(0,4,1),
    minor_breaks = NULL) + 
  geom_segment(data = edge,
    aes(x = ord1, y = brand1, xend = ord2, yend = brand2), 
    color = "blue", size = edge$N2/edge$N1) +
  ylim(lev) +
  theme_bw()

I get this plot, as expected.

我想添加另一个与线段宽度和 N2/N1 有关的图例（在节点下方）。

PD： 根据您的一些建议...

ggplot() + 
  geom_segment(data = edge,
    aes(x = ord1, y = brand1, xend = ord2, yend = brand2, size = N2/N1), 
    color = "blue", show.legend = T) +
  geom_point(data = nodes,
    aes(x = ord, y = brand, size = thick),
    color = "black", shape = 16, show.legend = T) + 
  scale_x_continuous(limits = c(1, 4), breaks = 0:4,
    minor_breaks = NULL) +
  scale_size_continuous(trans = "sqrt", breaks = c(1,4,9,16))  + 
  ylim(lev) +  theme_bw()

我得到了图例，但它与另一个重叠。

我可以尝试使用颜色而不是宽度：

ggplot()+ geom_segment(data=edge, aes(x=ord1, y=brand1, xend=ord2, yend=brand2, alpha=N2/N1) , size=1 ,show.legend = T) +
  geom_point(data=nodes,aes(x=ord, y=brand, size=thick), color="black", shape=16,show.legend = T) + 
  scale_x_continuous(limits=c(1, 4), breaks=seq(0,4,1), minor_breaks = NULL) + scale_size_continuous(trans = "sqrt", breaks=c(1,4,9,16))  + 
   ylim(lev) + theme_bw()

Or varying alpha

尽管我更喜欢原始的宽度方法，因为在我的真实图中，我会有很多线交叉。

PD：任何带有点阵的解决方案或任何能够导出为 svg 或矢量 pdf 的替代方案？

PD2：我发现了另一个问题，细点没有正确缩放，有时不可能强制 ggplot 显示正确的图例：如何强制 ggplot 在图例上显示更多级别？

Using a highly我整理的实验包：

library(ggplot2) # >= 2.3.0
library(dplyr)
library(relayer) # install.github("clauswilke/relayer")

# make aesthetics aware size scale, also use better scaling
scale_size_c <- function(name = waiver(), breaks = waiver(), labels = waiver(), 
          limits = NULL, range = c(1, 6), trans = "identity", guide = "legend", aesthetics = "size") 
{
  continuous_scale(aesthetics, "area", scales::rescale_pal(range), name = name, 
                   breaks = breaks, labels = labels, limits = limits, trans = trans, 
                   guide = guide)
}


lev <- c("A", "B", "C", "D")

nodes <- data.frame(
  ord = c(1,1,1,2,2,3,3,4),
  brand = factor(c("A", "B", "C", "B", "C", "D", "B", "D"), levels=lev), 
  thick = c(16, 9, 9, 16, 4, 1, 4, 1)
)

edge <- data.frame(
  ord1 = c(1, 1, 2, 3),
  brand1 = factor(c("C", "A", "B", "B"), levels = lev),
  ord2 = c(2, 2, 3, 4),
  brand2 = c("C", "B", "B", "D"),
  N1 = c(2, 1, 2, 1),
  N2 = c(5, 5, 2, 1)
)

ggplot() + 
  (geom_segment(
    data = edge,
    aes(x = ord1, y = brand1, xend = ord2, yend = brand2, edge_size = N2/N1), 
    color = "blue"
  ) %>% rename_geom_aes(new_aes = c("size" = "edge_size"))) +
  (geom_point(
    data = nodes,
    aes(x = ord, y = brand, node_size = thick),
    color = "black", shape = 16
  ) %>% rename_geom_aes(new_aes = c("size" = "node_size"))) + 
  scale_x_continuous(
    limits = c(1, 4),
    breaks = 0:4,
    minor_breaks = NULL
  ) +
  scale_size_c(
    aesthetics = "edge_size",
    breaks = 1:5,
    name = "edge size",
    guide = guide_legend(keywidth = grid::unit(1.2, "cm"))
  )  + 
  scale_size_c(
    aesthetics = "node_size",
    trans = "sqrt",
    breaks = c(1, 4, 9, 16),
    name = "node size"
  )  + 
  ylim(lev) + theme_bw()

创建于 2018-05-16代表包（v0.2.0）。