如何在时间序列中途改变ggplot2中的线属性？

Question

从economics{ggplot2}数据集中获取以下两个时间序列的简单图表

require(dplyr)
require(ggplot2)
require(lubridate)
require(tidyr)

economics %>%
  gather(indicator, percentage, c(4:5), -c(1:3, 6)) %>%
  mutate(Y2K = year(date) >= 2000) %>%
  group_by(indicator, Y2K) %>%
  ggplot(aes(date, percentage, group = indicator, colour = indicator)) + geom_line(size=1)

我想将21世纪所有点的linetype"固体"改为"虚线"(也可能是线size),即对于那些Y2K等于的观察TRUE.

我做了一个group_by(indicator, Y2K)但是在ggplot命令里面看来我不能group =在多个级别上使用,所以行属性indicator现在只有不同.

问题:如何实现这种分段线条外观？

更新:我的首选解决方案是@sahoang的轻微调整:

economics %>%
        gather(indicator, percentage, c(4:5), -c(1:3, 6)) %>%
        ggplot(aes(date, percentage, colour = indicator)) + 
        geom_line(size=1, aes(linetype = year(date) >= 2000)) +
        scale_linetype(guide = F)

这消除了group_by@Roland所评论的,并且filter步骤确保时间序列将在Y2K点处连接(如果数据是基于年份的,则可能存在视觉上的不连续性).

Answer 1

比@Roland的建议更容易:

economics %>%
    gather(indicator, percentage, c(4:5), -c(1:3, 6)) %>%
    mutate(Y2K = year(date) >= 2000) %>%
    group_by(indicator, Y2K) -> econ

ggplot(econ, aes(date, percentage, group = indicator, colour = indicator)) + 
  geom_line(data = filter(econ, !Y2K), size=1, linetype = "solid") + 
  geom_line(data = filter(econ, Y2K), size=1, linetype = "dashed")

PS更改绘图宽度以消除尖峰伪影(红线).