有没有一种方法可以在 ggplot2 中设置圆环图的 theta 轴刻度？

Question

我想在 ggplot2 poar 图中显示 theta 轴的刻度线。但是，theta 轴中的axis.ticks.y 和axis.ticks.y 都不适用于theta 轴。任何帮助将不胜感激，谢谢

library(ggplot2)
df <- data.frame(
    start = c(0, 121, 241),
    end = c(120, 240, 359),
    group = letters[1:3]
)
# a example circular ring plot
base <- ggplot(df, aes(ymax = end, ymin = start, 
                       xmin = 0.8, xmax = 1, 
                       fill = group)) +
    geom_rect() +
    coord_polar(theta = "y") +
    xlim(c(0, 1))
base

# the tick of y axis can be changed
base + theme(axis.ticks.y = element_blank(), axis.text.y = element_blank())

# set the tick of x axis not worked for the theta axis
base + theme(axis.ticks.x = element_line(color = "black", size = 2))

感谢@Vishal A.，Controlling ticks and odd text in a pie chart generated from a factor variable in ggplot2 的回答使用了panel.grid.major.y。但是，它将添加主要网格而不是像下面这样的刻度：

base + theme(panel.grid.major.y = element_line(colour = "black"))

^{由reprex package (v2.0.1) 于 2021 年 12 月 20 日创建}

Answer 1

您需要使用panel.grid.minor.y 而不是axis.ticks.y 才能更改刻度。 您的代码将如下所示：

base + theme(axis.ticks.y = element_blank(), axis.text.y = element_blank())
base + theme(panel.grid.minor.y = element_line(color = "black", size = 1))

输出将如下所示：

Answer 2

我看到两个选项。您可以使用面板网格，但您需要隐藏它们。此解决方案的有用性取决于您预期的情节背景。我用的是白色的，当然这可以定制。

第二个选项是使用注释来伪造刻度，例如，使用符号“|”。

下面的代码中还有更小的 cmets。

library(tidyverse)
df <- data.frame(
  start = c(0, 121, 241),
  end = c(120, 240, 359),
  group = letters[1:3]
)

ggplot(df) +
  ## annotate with a rectangle, effectively covering your central hole
  annotate(geom = "rect", xmin = 0, xmax = 1, ymin = min(df$start), ymax = max(df$end),
           fill = "white") +
  ## move aes to the geom_layer 
  geom_rect(aes(ymax = end, ymin = start, 
                xmin = 0.8, xmax = 1, 
                fill = group)) +
  coord_polar(theta = "y") +
  xlim(c(0, 1)) +
  theme(panel.grid.major.y = element_line(colour = "black"))

  
## Option 2 - fake the ticks
## the position along the theta axis is defined by y
## you need to change the angle of your fake ticks according to the angle. 
df_annot <- 
  data.frame(y = seq(0,300,100), x = Inf, angle = 360-seq(0,300,100))

ggplot(df) +
  ## annotate with text, along your y
  ## by placing it beneath your geom_rect layer it will automatically be covered 
  geom_text(data = df_annot, aes(x, y, label = "|", angle = angle)) +
  ## move aes to the geom_layer 
  geom_rect(aes(ymax = end, ymin = start, 
                xmin = 0.8, xmax = 1, 
                fill = group)) +
  coord_polar(theta = "y") +
  xlim(c(0, 1)) 

^{由reprex package (v2.0.1) 于 2021 年 12 月 21 日创建}