How to add label to geom_segment at the start of the segment?

问题

I'm sure this is simple but I can't figure it out.

I have the following chart:

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")

But I would like the labels to be off the axis and on the page. Either to the left or on top of the middle of the line. E.g.

Most of the examples of geom_text give me gobbledeegook. I can't seem to apply them to the factor data I have here. Do you know how to do this? Thank you

回答1:

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())

You need to use element_blank() to remove the y axis elements and then use nudge_x argument in geom_label to offset the labels appropriately.

回答2:

Having the labels on the end of the segments might distort the visual mapping of segment length and location to year-range. You could put the labels in the middle of the segments instead.

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())

Or what about going minimal:

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()

来源：https://stackoverflow.com/questions/45112019/how-to-add-label-to-geom-segment-at-the-start-of-the-segment

标签

ggplot2