使用scale_color_manual控制多数据组图例的点线样式与颜色

问题描述 #

此前在facet_wrap中为同一子集添加多条回归线时，遇到图例显示异常：需要Source组仅显示指定色盲友好配色的点（无连线），Fit组仅显示黑色回归线（无点），但现有代码运行后出现两种问题：

• 未设置stat_smooth的color时，Fit组图例呈现彩色连线；
• 设置stat_smooth的color="black"后，Source组图例出现黑色连线，且Fit组图例有点状标记。

原始代码 #

output_df <- data.frame(year=c(1993,1993,1995,1995,1998,1998,2001,2001,
                               1993,1993,1995,1995,1998,1998,2001,2001),
                        treatment_scen=c("CR","CR","CR","CR","CR","CR","CR","CR",
                                         "NT","NT","NT","NT","NT","NT","NT","NT"),
                        val=c(7.16875,22.60000,23.03250,24.30000,
                              29.46125,23.60000,21.41375,24.80000,
                              9.11125,25.30000,27.13950,26.60000,
                              30.46950,24.90000,24.60500,26.10000),
                        Source=c("Observed","Model","Observed","Model",
                                 "Observed","Model","Observed","Model",
                                 "Observed","Model","Observed","Model",
                                 "Observed","Model","Observed","Model")
                        )

trendlines_df <- data.frame(year=c(1993,1993,1995,1995,
                                   1998,1998,2001,2001,
                                   1993,1993,1995,1995,
                                   1998,1998,2001,2001),
                            treatment_scen=c("CR","CR","CR","CR",
                                        "CR","CR","CR","CR",
                                        "NT","NT","NT","NT",
                                        "NT","NT","NT","NT"),
                            Fit=c("AllObs","OutlierRemoved","AllObs","OutlierRemoved",
                                  "AllObs","OutlierRemoved","AllObs","OutlierRemoved",
                                  "AllObs","OutlierRemoved","AllObs","OutlierRemoved",
                                  "AllObs","OutlierRemoved","AllObs","OutlierRemoved"),
                            value=c(7.16875,NA,23.03250,23.03250,
                                    29.46125,29.46125,21.41375,21.41375,
                                    9.11125,NA,27.13950,27.13950,
                                    30.46950,30.46950,24.60500,24.60500),
                            Source=c("Observed","Observed","Observed","Observed",
                                     "Observed","Observed","Observed","Observed",
                                     "Observed","Observed","Observed","Observed",
                                     "Observed","Observed","Observed","Observed"),
                            Model=c("Observed","Observed","Observed","Observed",
                                     "Observed","Observed","Observed","Observed",
                                     "Observed","Observed","Observed","Observed",
                                     "Observed","Observed","Observed","Observed")
)

# 9-color palette with grey and black. Colors in order are:
#[1]black, [2]dark blue, [3]green, [4]light blue, [5]grey,
#[6]pink, [7]red, [8]orange, [9]yellow
cbPalette9 <- c("#000000","#0072B2","#009E73","#56B4E9","#999999",
                "#CC79A7","#D55E00","#E69F00","#F0E442")

 
g1 <- output_df %>%
  ggplot(aes(x=year, y=val, color=Source, show.legend=TRUE)) +
  geom_point(show.legend=TRUE) +
  xlab("Year") +
  stat_smooth(
    data = trendlines_df, 
    aes(linetype = Fit, y=value), 
    #color="black", 
    method = lm,
    se = FALSE,
    show.legend = TRUE,
    fullrange=TRUE
  ) +
  scale_color_manual(labels=c("Model","Observed"),
                     values=cbPalette9[c(8,3)]) +
  facet_wrap(~treatment_scen,nrow=1) 

g1

异常效果 #

• 未设置黑色线条时的输出：
  

• 设置黑色线条后的输出：
  

解决方案 #

核心思路是分离点和线条的美学映射，并通过guides()定制图例显示：

1. 将color=Source的映射从全局aes移到geom_point中，避免stat_smooth继承颜色映射；
2. 固定stat_smooth的线条颜色为黑色；
3. 分别对两个图例进行外观覆盖，确保Source图例仅显示点，Fit图例仅显示黑色线条。

修改后的代码：

g1 <- output_df %>%
  ggplot(aes(x=year, y=val)) +  # 全局aes仅保留x、y，去掉color映射
  geom_point(aes(color=Source), show.legend=TRUE) +  # 点单独绑定color=Source
  xlab("Year") +
  stat_smooth(
    data = trendlines_df, 
    aes(linetype = Fit, y=value), 
    color="black",  # 固定回归线为黑色
    method = lm,
    se = FALSE,
    show.legend = TRUE,
    fullrange=TRUE
  ) +
  scale_color_manual(labels=c("Model","Observed"),
                     values=cbPalette9[c(8,3)]) +
  facet_wrap(~treatment_scen,nrow=1) +
  guides(
    # 定制Source图例：仅显示点，移除连线
    color = guide_legend(override.aesthetics = list(linetype = "blank")),
    # 定制Fit图例：仅显示黑色线条，移除点标记
    linetype = guide_legend(override.aesthetics = list(color = "black", shape = NA))
  )

g1

效果说明 #

修改后：

• Source图例仅显示指定配色的点状标记，无多余连线；
• Fit图例仅显示黑色的不同线型，无点状标记；
• 图中回归线保持黑色，点的颜色符合色盲友好配色要求。

内容的提问来源于stack exchange，提问作者E Maas