在ggplot2图中添加曲形文字注释

在现有的ggplot2绘图系统中，使用geom_text和geom_label 在已有的图层上添加文字、标签，是大多数图的理想选择。通常情况下，geom_text和geom_label适用于文本长度较短，并且与轴的方向保持一致的注释。但是，在某些情况下，使文本遵循弯曲的路径很有用，它可以展现出更加自然的视觉效果。

基于ggplot2绘图系统的geomtextpath包可以实现以上功能。 geomtextpath整合了绘图函数与文本标签，将文本附着在其关联的图形元素上，既能保持与图形元素相同的曲线形状，又无需指定确切的标签位置，具有较低的超标风险。

# 安装`geomtextpath`

# install.packages("remotes")
remotes::install_github("AllanCameron/geomtextpath")

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# 使用`geomtextpath`

参考文档 (opens new window)

# `geom_textline` and `geom_labelline`

ggplot(pressure, aes(temperature, pressure)) +
  geom_textline(label = "Mercury vapor pressure", size = 6, vjust = -0.5,
                linewidth = 1, linecolor = "red4", linetype = 2, 
                color = "deepskyblue4")

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# `geom_textdensity` and `geom_labeldensity`

ggplot(iris, aes(x = Sepal.Length, colour = Species, label = Species)) +
  geom_textdensity(size = 6, fontface = 2, hjust = 0.2, vjust = 0.3) +
  theme(legend.position = "none")

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# Reference Line

ggplot(mtcars, aes(mpg, disp)) + 
  geom_point() + 
  geom_texthline(yintercept = 200, label = "displacement threshold", 
                 hjust = 0.8, color = "red4") +
  geom_textvline(xintercept = 20, label = "consumption threshold", hjust = 0.8,
                 linetype = 2, vjust = 1.3, color = "blue4") +
  geom_textabline(slope = 15, intercept = -100, label = "partition line", 
                  color = "green4", hjust = 0.6, vjust = -0.2)

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# `geom_textpath`与极坐标系很好的融合

p <- data.frame(x1 = c(seq(0, 10/6 * pi, pi/3),
                  seq(0, 10/6 * pi, 2*pi/3)),
           y1 = c(rep(2, 6), rep(-1, 3)),
           x2 = c(seq(0, 10/6 * pi, pi/3)  + pi/3,
                  seq(0, 10/6 * pi, 2*pi/3) + 2*pi/3),
           y2 = c(rep(4, 6), rep(2, 3)),
           group = letters[c(1:6, (1:3) * 2)],
           alpha = c(rep(1, 6), rep(0.4, 3))) |>
  ggplot(aes(x1, y1)) +
  geom_rect(aes(xmin = x1, xmax = x2, ymin = y1, ymax = y2, fill = group,
                alpha = alpha),
            color = "white", size = 2) +
  geom_textpath(data = data.frame(x1 = seq(0, 2 * pi, length = 300),
           y1 = rep(0.5, 300),
           label = rep(c("stats", "effects", "polar"), each = 100)),
           aes(label = label), linetype = 0, size = 8,
           upright = TRUE) +
  geom_textpath(data = data.frame(x1 = seq(0, 2 * pi, length = 300),
           y1 = rep(3, 300),
           label = rep(c("density", "smooth", "unique", "organic",
                         "easy to use", "automatic"), 
                       each = 50)),
           aes(label = label), linetype = 0, size = 4.6, color = "white",
           upright = TRUE) +
  scale_y_continuous(limits = c(-5, 4)) +
  scale_x_continuous(limits = c(0, 2*pi)) +
  scale_fill_manual(values = c("deepskyblue3", "deepskyblue4",
                               "green3", "green4","tomato", "tomato2")) +
  scale_alpha_identity() +
  theme_void() +
  theme(legend.position = "none") 

p