如何统一ggplot2子图图例，仅显示模型对应颜色的点？

我需要在每个子图中为三个模型（A/B/C）绘制不同颜色的loess拟合曲线，但当前代码生成的图例同时混合了点和线，希望图例只保留不同颜色的点，对应三个模型。

原代码如下：

mydata1 <- data.frame("model" = rep("A", 1000), "n" = sample.int(10, 1000, replace = T), "n1" = seq(1,1000), "values" = rnorm(1000))
mydata2 <- data.frame("model" = rep("B", 1000), "n" = sample.int(10, 1000, replace = T), "n1" = seq(1,1000), "values" = rnorm(1000))
mydata3 <- data.frame("model" = rep("C", 500), "n" = c(rep(6,100),rep(7,100),rep(8,100),rep(9,100),rep(10,100)), "n1" = seq(1,500), "values" = rnorm(500))
mydata <- rbind(mydata1, mydata2, mydata3)

fig_list <- list()
for (i in sort(unique(mydata$n))) {
   data <- mydata[mydata$n == i, ]
   fig_list[[i]] <- ggplot(data, aes(x = n1, y = values, colour = model)) +
           geom_point(size = 0.6, show.legend = TRUE) +
           scale_color_discrete(limits = unique(mydata$model)) +
           labs(title = paste0("n = ", i), x = "n1", y = "values") +
           theme(plot.title = element_text(hjust = 0.5, size = 10)) + 
           geom_smooth(method = "loess", span = 0.3, fill = "lightskyblue", level = 0.95) 
}

fig_all <- ggarrange(
     plotlist = fig_list, ncol = 2, nrow = ceiling(length(fig_list) / 2),
     common.legend = TRUE, legend = "top"
)
annotate_figure(fig_all, top = text_grob(paste0("All the plots are here.")))

只需对geom_smooth进行修改，阻止它生成图例元素，同时确保geom_point的图例正常显示：

1. 在geom_smooth中添加show.legend = FALSE参数，让拟合曲线不参与图例的构建
2. 保持geom_point的show.legend = TRUE，确保图例只展示模型对应的颜色点

修改后的完整代码：

mydata1 <- data.frame("model" = rep("A", 1000), "n" = sample.int(10, 1000, replace = T), "n1" = seq(1,1000), "values" = rnorm(1000))
mydata2 <- data.frame("model" = rep("B", 1000), "n" = sample.int(10, 1000, replace = T), "n1" = seq(1,1000), "values" = rnorm(1000))
mydata3 <- data.frame("model" = rep("C", 500), "n" = c(rep(6,100),rep(7,100),rep(8,100),rep(9,100),rep(10,100)), "n1" = seq(1,500), "values" = rnorm(500))
mydata <- rbind(mydata1, mydata2, mydata3)

fig_list <- list()
for (i in sort(unique(mydata$n))) {
   data <- mydata[mydata$n == i, ]
   fig_list[[i]] <- ggplot(data, aes(x = n1, y = values, colour = model)) +
           geom_point(size = 0.6, show.legend = TRUE) +
           scale_color_discrete(limits = unique(mydata$model)) +
           labs(title = paste0("n = ", i), x = "n1", y = "values") +
           theme(plot.title = element_text(hjust = 0.5, size = 10)) + 
           # 添加show.legend = FALSE，隐藏拟合曲线的图例元素
           geom_smooth(method = "loess", span = 0.3, fill = "lightskyblue", level = 0.95, show.legend = FALSE) 
}

fig_all <- ggarrange(
     plotlist = fig_list, ncol = 2, nrow = ceiling(length(fig_list) / 2),
     common.legend = TRUE, legend = "top"
)
annotate_figure(fig_all, top = text_grob(paste0("All the plots are here.")))

补充说明 #

如果需要进一步确保图例只显示点（避免其他潜在元素干扰），可以在ggplot中添加guides()参数，强制图例隐藏线的样式：

fig_list[[i]] <- ggplot(data, aes(x = n1, y = values, colour = model)) +
    geom_point(size = 0.6, show.legend = TRUE) +
    scale_color_discrete(limits = unique(mydata$model)) +
    labs(title = paste0("n = ", i), x = "n1", y = "values") +
    theme(plot.title = element_text(hjust = 0.5, size = 10)) + 
    geom_smooth(method = "loess", span = 0.3, fill = "lightskyblue", level = 0.95, show.legend = FALSE) +
    # 强制图例只显示点，不显示线
    guides(colour = guide_legend(override.aes = list(linetype = "blank")))

内容的提问来源于stack exchange，提问作者Phoebe