如何在双 y 轴 ggplot 上显示图例 [英] how to show a legend on dual y-axis ggplot

问题描述

我正在尝试使用 ggplot 制作双 y 轴图表.首先让我说，我不是在寻求关于这样做是否是好的做法的优点的讨论.我发现它们在查看基于时间的数据以识别 2 个离散变量的趋势时特别有用.在我看来，对此的进一步讨论更适合交叉验证.

I am trying to compose a dual y-axis chart using ggplot. Firstly let me say that I am not looking for a discussion on the merits of whether or not it is good practice to do so. I find them to be particularly useful when looking at time based data to identify trends in 2 discrete variables. A further discussion of this is better suited to crossvalidated in my opinion.

Kohske 提供了一个很好的例子来说明如何做到这一点，我已经用过它，效果很好迄今为止.但是，我无法为两个 y 轴都包含一个图例.我也看到过类似的问题 此处 和此处 但似乎没有解决包含图例的问题.

Kohske provides a very good example of how to do it, which I have used to great effect so far. I am however at my limits to include a legend for both y-axes. I have also seen similar questions here and here but none seem to address the issue of including a legend.

我有一个使用来自 ggplot 的钻石数据集的可重现示例.

I've got a reproduceable example using the diamonds dataset from ggplot.

数据

library(ggplot2)
library(gtable)
library(grid)
library(data.table)
library(scales)

grid.newpage()

dt.diamonds <- as.data.table(diamonds)

d1 <- dt.diamonds[,list(revenue = sum(price),
                        stones = length(price)),
                  by=clarity]

setkey(d1, clarity)

图表

p1 <- ggplot(d1, aes(x=clarity,y=revenue, fill="#4B92DB")) +
  geom_bar(stat="identity") +
  labs(x="clarity", y="revenue") +
  scale_fill_identity(name="", guide="legend", labels=c("Revenue")) +
  scale_y_continuous(labels=dollar, expand=c(0,0)) + 
  theme(axis.text.x = element_text(angle = 90, hjust = 1),
        axis.text.y = element_text(colour="#4B92DB"), 
        legend.position="bottom")

p2 <- ggplot(d1, aes(x=clarity, y=stones, colour="red")) +
  geom_point(size=6) + 
  labs(x="", y="number of stones") + expand_limits(y=0) +
  scale_y_continuous(labels=comma, expand=c(0,0)) +
  scale_colour_manual(name = '',values =c("red","green"), labels = c("Number of Stones"))+
  theme(axis.text.y = element_text(colour = "red")) +
  theme(panel.background = element_rect(fill = NA),
        panel.grid.major = element_blank(),
        panel.grid.minor = element_blank(),
        panel.border = element_rect(fill=NA,colour="grey50"),
        legend.position="bottom")

# extract gtable
g1 <- ggplot_gtable(ggplot_build(p1))
g2 <- ggplot_gtable(ggplot_build(p2))


pp <- c(subset(g1$layout, name == "panel", se = t:r))
g <- gtable_add_grob(g1, g2$grobs[[which(g2$layout$name == "panel")]], pp$t,
                     pp$l, pp$b, pp$l)
# axis tweaks
ia <- which(g2$layout$name == "axis-l")
ga <- g2$grobs[[ia]]
ax <- ga$children[[2]]
ax$widths <- rev(ax$widths)
ax$grobs <- rev(ax$grobs)
ax$grobs[[1]]$x <- ax$grobs[[1]]$x - unit(1, "npc") + unit(0.15, "cm")
g <- gtable_add_cols(g, g2$widths[g2$layout[ia, ]$l], length(g$widths) - 1)
g <- gtable_add_grob(g, ax, pp$t, length(g$widths) - 1, pp$b)
# draw it
grid.draw(g)

问题:有人对如何显示图例的第二部分有一些提示吗?

QUESTION: Does anyone have some tips on how to get the 2nd part of the legend to show?

以下是按照 p1、p2、组合 p1&p2 的顺序生成的图表，您会注意到 p2 的图例未显示在组合图表中.

The following are the charts produced in order p1, p2, combined p1&p2, you'll notice that the legend for p2 doesn't show in the combined chart.

p1

p2

结合 p1 &p2

推荐答案

与您上面使用的技术类似，您可以提取图例，绑定它们，然后用它们覆盖情节图例.

Similar to the technique you use above you can extract the legends, bind them and then overwrite the plot legend with them.

所以从 # draw it 在你的代码开始

So starting from # draw it in your code

# extract legend
leg1 <- g1$grobs[[which(g1$layout$name == "guide-box")]]
leg2 <- g2$grobs[[which(g2$layout$name == "guide-box")]]

g$grobs[[which(g$layout$name == "guide-box")]] <- 
                                  gtable:::cbind_gtable(leg1, leg2, "first")
grid.draw(g)

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