如何在ggplot2中绘制一个漂亮的箭头

Question

我正在创建一个ggplot图表,我希望在两点之间有一些箭头.主要任务很容易完成geom_line(arrow = arrow()).但是,我想要一些"漂亮"的粗箭.调整箭头的大小size=没有用,因为它完全弄乱了箭头.我说明了我的问题:

创建一些示例数据和图:

 NAME <- c("A", "A", "B", "B", "C", "C")
 YEAR <- c(2016, 2011, 2016, 2011, 2016, 2011)
 YEAR <- as.factor(YEAR)
 VALUE <- c(1, 4, 1, 5, 2, 8)
 DATA <- data.frame(NAME, YEAR, VALUE)

ggplot(DATA, aes(x=VALUE, y=NAME)) + 
  geom_point(size=5, aes(colour=YEAR)) +
  geom_line(arrow = arrow(length=unit(0.30,"cm"), ends="first", type = "closed"))

结果图看起来像这样:

现在我试图"加厚"箭头......

ggplot(DATA, aes(x=VALUE, y=NAME)) + 
  geom_point(size=5, aes(colour=YEAR)) +
  geom_line(arrow = arrow(length=unit(0.30,"cm"), ends="first", type = "closed"), size = 3)

这是这里显示的结果:

我的问题:有没有办法绘制一些"美丽的"粗箭？

Answer 1

以下是一些可重现的示例（尝试运行它们）

一个简单的箭头（即线段）：

library(dplyr)
library(ggplot2)

# Create a scatter plot
i <- ggplot(mtcars, aes(wt, mpg)) + geom_point()

# Add arrow
i + geom_segment(aes(x = 5, y = 30, xend = 3.5, yend = 25),
                  arrow = arrow(length = unit(0.5, "cm")))

一个简单的弯曲箭头

b <- ggplot(mtcars, aes(wt, mpg)) +
  geom_point()

df <- data.frame(x1 = 2.62, x2 = 3.57, y1 = 21.0, y2 = 15.0)

b + geom_curve(
  aes(x = x1, y = y1, xend = x2, yend = y2),
  data = df,
  arrow = arrow(length = unit(0.03, "npc"))
)

可用的箭头类型

您不必理解此代码，只需注意可用的lineend, 和linejoin选项

df2 <- expand.grid(
  lineend = c('round', 'butt', 'square'),
  linejoin = c('round', 'mitre', 'bevel'),
  stringsAsFactors = FALSE
)
df2 <- data.frame(df2, y = 1:9)

ggplot(df2, aes(x = 1, y = y, xend = 2, yend = y, label = paste(lineend, linejoin))) +
  geom_segment(
    lineend = df2$lineend, linejoin = df2$linejoin,
    size = 3, arrow = arrow(length = unit(0.3, "inches"))
  ) +
  geom_text(hjust = 'outside', nudge_x = -0.2) +
  xlim(0.5, 2)

为自己切换的直箭头

这是一个非常简单的箭头来调整每个参数并查看它的作用

ggplot(iris) +
  geom_segment(
    x = 1, y = 1,
    xend = 4, yend = 7,
    lineend = "round", # See available arrow types in example above
    linejoin = "round",
    size = 2, 
    arrow = arrow(length = unit(0.3, "inches")),
    colour = "#EC7014" # Also accepts "red", "blue' etc
  ) + 
  scale_x_continuous(limits = c(0, 10)) +
  scale_y_continuous(limits = c(0, 10))

为自己切换的弯曲箭头

# Nicer curve
b <- ggplot(mtcars, aes(wt, mpg)) +
  geom_point()

b + geom_curve(
  aes(x = 3, y = 22, xend = 3.5, yend = 15),
  arrow = arrow(
    length = unit(0.03, "npc"), 
                type="closed" # Describes arrow head (open or closed)
    ),
  colour = "#EC7014",
  size = 1.2,
  angle = 90 # Anything other than 90 or 0 can look unusual
)

Answer 2

我通常geom_segment用来创造箭头.但要做到这一点,我们需要将数据从"长"格式修改为"宽"格式(通常使用dcastfrom reshape2或data.tablepackage).但这次我尝试使用base的reshape功能.

ggplot(DATA, aes(x=VALUE, y=NAME)) + 
  geom_point(size=5, aes(colour=YEAR)) +
  geom_segment(data = reshape(DATA, v.names="VALUE", idvar = "NAME", timevar = "YEAR", direction = "wide"),
               aes(x=VALUE.2011, xend=VALUE.2016, y=NAME, yend=NAME), size = 2,
               arrow = arrow(length = unit(0.5, "cm")))

编辑:我刚刚发现同样的问题属于"封闭"类型的箭头.现在,尝试将绘图保存为矢量图(pdf或svg,使用ggsave"绘图"选项卡中的"导出"菜单).结果不是"凌乱".

Answer 3

在最新的(我的意思是devtools::install_github("tidyverse/ggplot2")最新的,截至写这个答案 - 我敢肯定他们很快就会主题化)版本ggplot2,有一个linejoin论据geom_segment.使用linejoin='mitre'将提供清晰的边缘.查看详细信息如下.