如何在ggplot2中将填充图例设为涂抹状而非预定义形状？

首先是用户提供的数据集：

df <- structure(list(Fruit = c("Apple", "Orange", "Graphe", "Apple", "Orange", "Graphe", "Apple", "Orange", "Graphe", "Apple", "Orange", "Graphe", "Apple", "Orange", "Graphe", "Apple", "Orange", "Graphe", "Apple", "Orange", "Graphe", "Apple", "Orange", "Graphe", "Apple", "Orange", "Graphe", "Apple", "Orange", "Graphe"), value1 = c(9L, 27L, 21L, 13L, 30L, 8L, 29L, 24L, 25L, 10L, 20L, 5L, 1L, 28L, 11L, 3L, 4L, 12L, 26L, 14L, 19L, 16L, 6L, 17L, 23L, 7L, 18L, 22L, 15L, 2L), value2 = c(11L, 6L, 1L, 30L, 2L, 12L, 20L, 27L, 3L, 10L, 26L, 4L, 7L, 8L, 15L, 5L, 17L, 21L, 18L, 9L, 19L, 16L, 24L, 14L, 23L, 22L, 29L, 13L, 25L, 28L), Var = c("A", "A", "A", "A", "B", "B", "B", "B", "B", "B", "A", "B", "B", "A", "A", "A", "B", "B", "A", "A", "A", "B", "B", "A", "B", "A", "B", "A", "A", "A")), class = "data.frame", row.names = c(NA, -30L))

用户的原始绘图代码：

library(ggplot2)

ggplot(df, aes(value1, value2, fill = Var, shape = Fruit)) + 
  geom_point(color = "black", size = 2.5) +
  scale_shape_manual(values = 21:23) +
  guides(fill = guide_legend("Identity", override.aes = list(shape = 21)))

完全可以通过key_glyph参数结合自定义函数实现污渍/涂抹状的填充图例，具体步骤如下：

• 自定义污渍形状的key glyph函数
  利用grid包的绘图工具生成不规则的污渍图形，这里通过随机多边形模拟自然的污渍边缘：

library(grid)

# 自定义污渍图例生成函数
glyph_stain <- function(data, params, size) {
  # 生成10个随机角度的边缘点
  n_points <- 10
  angles <- seq(0, 2*pi, length.out = n_points)
  # 随机半径，控制污渍的不规则程度
  radii <- runif(n_points, min = 0.3, max = 0.5) * size
  
  x <- radii * cos(angles)
  y <- radii * sin(angles)
  
  # 创建多边形图形对象
  polygonGrob(
    x = x, y = y,
    gp = gpar(
      fill = data$fill,
      col = data$colour %||% "black",
      lwd = data$size %||% 0.5
    )
  )
}

• 在绘图中应用自定义图例
  将自定义函数传入guide_legend的key_glyph参数，替换fill图例的默认形状：

ggplot(df, aes(value1, value2, fill = Var, shape = Fruit)) + 
  geom_point(color = "black", size = 2.5) +
  scale_shape_manual(values = 21:23) +
  guides(
    fill = guide_legend(
      title = "Identity",
      key_glyph = glyph_stain  # 使用自定义污渍图例
    ),
    shape = guide_legend(title = "Fruit")
  )

额外调整建议 #

• 若想让污渍更自然，可增加n_points的数值（比如15），或调整radii的范围（比如min=0.2, max=0.6）；
• 也可以用pathGrob结合贝塞尔曲线绘制更流畅的不规则边缘，或者导入外部污渍SVG转为Grob对象使用。

内容的提问来源于stack exchange，提问作者benson23