如何在段的开头向 geom_segment 添加标签？

Question

我确定这很简单，但我想不通。

我有以下图表：

library(data.table)
library(magrittr)
library(ggplot2)

cambodia <- 
    data.table(Period = c("Funan", "Chenla/Zhenla","Khmer Empire","Dark Ages of Cambodia"),
               StartDate = c(-500,550,802,1431), 
               EndDate = c(550,802,1431,1863), 
               Color = c("lightblue","lightgreen","lightyellow","pink")) %>%
    extract(order(-StartDate)) %>%
    extract(, Period := factor(Period,levels = Period))

ggplot() +
    geom_segment(data=cambodia, aes(x=StartDate, xend=EndDate, y=Period, yend=Period, color=Color), 
                 linetype=1, size=2) +
    scale_colour_brewer(palette = "Pastel1")+
    xlab("Date")+
    ylab("Ruler")+
    theme_bw() + 
    theme(panel.grid.minor = element_blank(), panel.grid.major =   element_blank()) + 
    theme(aspect.ratio = .2) +
    theme(legend.position="none")

但我希望标签不在轴上并在页面上。在线的左边或中间的顶部。例如

geom_text 的大多数示例都给了我 gobbledeegook。我似乎无法将它们应用于我在这里拥有的因子数据。你知道怎么做吗？ 谢谢

Answer 1

在片段末尾添加标签可能会扭曲片段长度和位置到年份范围的视觉映射。您可以将标签放在段的中间。

library(data.table)
library(magrittr)
library(ggplot2)
library(stringr)

cambodia <- 
  data.table(Period = c("Funan", "Chenla/Zhenla","Khmer Empire","Dark Ages of Cambodia"),
             StartDate = c(-500,550,802,1431), 
             EndDate = c(550,802,1431,1863), 
             Color = c("lightblue","lightgreen","lightyellow","pink")) %>%
  extract(order(-StartDate)) %>%
  extract(, Period := factor(Period,levels = Period))

ggplot(cambodia, aes(x=StartDate, xend=EndDate, y=Period, colour=Period)) +
  geom_segment(aes(xend=EndDate, yend=Period), linetype=1, size=2) +
  geom_label(aes(label=str_wrap(Period,12), x=(StartDate + EndDate)/2), size=3) +
  scale_colour_brewer(palette = "Set1") +
  xlab("Date")+ ylab("Ruler")+
  theme_bw() + 
  theme(panel.grid.minor = element_blank(), panel.grid.major = element_blank(), 
        aspect.ratio = .2,
        legend.position="none",
        axis.text.y=element_blank(),
        axis.ticks.y=element_blank())

或者如何做到最小化：

ggplot(cambodia, aes(x=StartDate, y=1)) +
  geom_rect(aes(xmin=StartDate, xmax=EndDate, ymin=0.97, ymax=1.03, fill=Period), 
            show.legend=FALSE, colour="white", size=0.5) +
  geom_label(aes(label=str_wrap(Period,12), x=(StartDate + EndDate)/2), size=3.5) +
  geom_text(aes(label=StartDate, y=0.96), size=3.5) +
  geom_text(aes(label=ifelse(EndDate==max(EndDate), EndDate,""), x=EndDate, y=0.96), size=3.5) +
  scale_colour_brewer(palette = "Set1") +
  scale_y_continuous(limits=c(0.95,1.05)) +
  theme_void() 

Answer 2

ggplot() +
  geom_segment(data=cambodia, aes(x=StartDate, xend=EndDate, y=Period, yend=Period, color=Color), 
               linetype=1, size=2) +
  geom_label(data=cambodia, aes(x=StartDate, y=Period,  label = Period),
             nudge_x = c(-300, -200, -200, -100)) +
  scale_colour_brewer(palette = "Pastel1")+
  xlab("Date")+
  ylab("")+
  theme_bw() + 
  theme(legend.position="none") +
  theme(aspect.ratio = .2) +
  theme(panel.grid.minor = element_blank(), panel.grid.major =   element_blank(),
        axis.line.y = element_blank(), axis.text.y = element_blank(),
        axis.ticks.y = element_blank())

您需要使用element_blank() 删除y 轴元素，然后使用geom_label 中的nudge_x 参数来适当地偏移标签。