ggplot：从同一点开始的多行

Question

我有一个像这样的数据集：

df <- data.frame(Species = c("Sp A", "Other sp", "Other sp", "Other sp",
                       "Sp A", "Other sp", "Other sp"), 
           Study = c("A", "A", "A", "A", 
                     "B", "B", "B"), 
           Value = c(1, 3, 4, 5, 3, 6, 7))

看起来像这样：

> df
   Species Study Value
1     Sp A     A     1
2 Other sp     A     3
3 Other sp     A     4
4 Other sp     A     5
5     Sp A     B     3
6 Other sp     B     6
7 Other sp     B     7

我想将物种A的值与同一研究中其他物种的值进行比较 这是我现在的情节：

ggplot(df, aes(y = Value, x = Species)) + 
    geom_point(shape = 1) +
    geom_line(aes(group = Study), color = "gray50") +
    theme_bw()

我不想要垂直线条。取而代之的是，我希望有5条线，3条从较低的“Sp A”点开始，朝向3条相应的“其他sp”点从同一研究（A）开始，2条从上部“Sp A”开始朝向来自同一研究的其他两点（B）。

Answer 1

可能有一种更优雅的方式，但这是一个有效的解决方案。诀窍是稍微重新排列数据，然后使用geom_segment：

library(tidyverse)
df <- data.frame(Species = c("Sp A", "Other sp", "Other sp", "Other sp",
                             "Sp A", "Other sp", "Other sp"), 
                 Study = c("A", "A", "A", "A", 
                           "B", "B", "B"), 
                 Value = c(1, 3, 4, 5, 3, 6, 7))

# Split data
other <- df %>% filter(Species == "Other sp")
sp_a <- df %>% filter(Species == "Sp A")

# Recombine into the data set for plotting
df <- other %>%
  inner_join(sp_a, by = "Study")

# Make the plot
ggplot(df, aes(x = Species.y, y = Value.y)) +
  geom_segment(aes(xend = Species.x, yend = Value.x, colour = Study))

根据需要调整图表！

Answer 2

如果对于geom_line的每个级别，您复制Study行的数量以匹配Sp A行的数量，然后分配，则可以使用Other sp执行此操作Sp A美学的每对Other Sp和group的唯一ID。

library(tidyverse)

df %>% group_by(Study) %>% 
  slice(c(rep(1,length(Species[Species=="Other sp"])),2:n())) %>%  
  group_by(Study, Species) %>% 
  mutate(ID = paste0(Study, 1:n())) %>% 
  ggplot(aes(y = Value, x=Species, group=ID, colour=Study)) + 
    geom_point(shape=1) +
    geom_line() +
    theme_bw()