ggplot2：为geom_path与geom_point组合图设置单个重命名图例

问题出在你同时使用了shape、fill、colour三个美学映射绑定同一分组变量，但仅修改了shape的图例标题，导致图例拆分。要合并成单个带"Sample"标题的图例，只需统一所有相关美学映射的图例名称即可，以下是两种简洁方法：

方法一：通过labs()统一设置所有相关美学的标题 #

直接在labs()里同时指定shape、fill、colour的标题为"Sample"，ggplot会自动将同变量的图例合并：

ggplot(great_hollow, aes(x = d15N, y = Sample_ordered)) + 
  geom_path(aes(group = Species_ordered, colour = Species_ordered)) +
  geom_point(aes(shape = Species_ordered, fill = Species_ordered), colour = "black", size = 3) +
  scale_shape_manual(values = c(21, 22, 24, 21, 23, 25)) +
  # 同时设置三个美学的图例标题为Sample
  labs(shape = "Sample", fill = "Sample", colour = "Sample") +
  facet_wrap(~Type, scales = "fixed") +
  ggtitle(expression(paste(delta^{15},"N Values by Site and Trophic Level"))) +
  scale_x_continuous(expression(paste(delta^{15}, "N (‰ VS air)"))) +
  scale_y_discrete(limits=rev) +
  theme_bw() +
  theme(plot.title = element_text(hjust = 0.5),
        axis.title.y = element_blank(),
        plot.background = element_rect(color = 1, linewidth = 1), 
        plot.margin = margin(t = 10,  
                             r = 10,  
                             b = 10, 
                             l = 10))

方法二：在手动scale中统一设置name参数 #

如果你需要手动指定fill和colour的颜色，可在对应的scale函数里设置name="Sample"，同时给shape的scale也设置名称，同样能合并图例：

ggplot(great_hollow, aes(x = d15N, y = Sample_ordered)) + 
  geom_path(aes(group = Species_ordered, colour = Species_ordered)) +
  geom_point(aes(shape = Species_ordered, fill = Species_ordered), colour = "black", size = 3) +
  # 给shape的scale设置名称
  scale_shape_manual(name = "Sample", values = c(21, 22, 24, 21, 23, 25)) +
  # 自定义颜色时可指定values，仅统一名称则留空values用默认配色
  scale_colour_manual(name = "Sample") +
  scale_fill_manual(name = "Sample") +
  facet_wrap(~Type, scales = "fixed") +
  ggtitle(expression(paste(delta^{15},"N Values by Site and Trophic Level"))) +
  scale_x_continuous(expression(paste(delta^{15}, "N (‰ VS air)"))) +
  scale_y_discrete(limits=rev) +
  theme_bw() +
  theme(plot.title = element_text(hjust = 0.5),
        axis.title.y = element_blank(),
        plot.background = element_rect(color = 1, linewidth = 1), 
        plot.margin = margin(t = 10,  
                             r = 10,  
                             b = 10, 
                             l = 10))

额外修正：初始aes语法错误 #

你原代码中ggplot(great_hollow, aes(x = d15N, y = Sample_ordered), color = Species_ordered)的color = Species_ordered写在了aes()外面，属于无效语法，已在上述代码中修正，将分组变量的映射放在对应geom的aes()内。

内容的提问来源于stack exchange，提问作者theyhem