如何修改ggplot2中ref点及对应误差棒的颜色？

需求说明 #

需要将ggplot2图表中标注为“ref”（对应数据集chan=11）的数据点及其误差棒修改为特定颜色，原绘图代码及数据集如下：

原绘图代码

ggplot(df,aes(x = chan,y = mean)) + 
    geom_errorbar(aes(ymin = mean - sd, ymax = mean + sd)) +
    geom_point() + 
    theme_bw() +
    ylab("accuracy") + 
    xlab("permutation channel") + 
    scale_x_continuous(breaks = c(1:11), labels = c(1:10, "ref"))

数据集结构

structure(list(chan = c(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11), mean = c(0.951002180576324, 
0.954477310180664, 0.954147934913635, 0.955366730690002, 0.945781230926514, 
0.95714545249939, 0.95810067653656, 0.951051592826843, 0.947444677352905, 
0.946522414684296, 0.9573002576828), sd = c(0.00134088819225075, 
0.00426092161364007, 0.00461019843766268, 0.00517772940490045, 
0.000785548183287362, 0.00274702164693839, 0.004252234407014, 
0.00353576303790188, 0.00276008055853283, 0.00427941769453181, 
0.00225555534939029)), row.names = c(NA, -11L), class = "data.frame")

两种简便解决方案 #

方案1：通过颜色映射实现（推荐，逻辑清晰）

先给数据集添加分组标记列区分“ref”和其他数据，再通过scale_color_manual自定义颜色：

# 给数据集添加分组列
df$group <- ifelse(df$chan == 11, "ref", "others")

# 修改绘图代码
ggplot(df,aes(x = chan,y = mean, color = group)) + 
    geom_errorbar(aes(ymin = mean - sd, ymax = mean + sd)) +
    geom_point() + 
    theme_bw() +
    ylab("accuracy") + 
    xlab("permutation channel") + 
    scale_x_continuous(breaks = c(1:11), labels = c(1:10, "ref")) +
    # 自定义颜色，others用默认黑色，ref用红色
    scale_color_manual(values = c("others" = "black", "ref" = "red")) +
    guides(color = "none") # 不需要图例可添加此行

方案2：单独绘制目标数据（无需修改原数据集）

直接在原有图层上，单独绘制chan=11对应的误差棒和点并设置指定颜色：

ggplot(df,aes(x = chan,y = mean)) + 
    # 先绘制所有数据的误差棒和点（默认颜色）
    geom_errorbar(aes(ymin = mean - sd, ymax = mean + sd)) +
    geom_point() + 
    # 单独绘制ref的误差棒和点，设置红色
    geom_errorbar(data = df[df$chan == 11,], aes(ymin = mean - sd, ymax = mean + sd), color = "red") +
    geom_point(data = df[df$chan == 11,], color = "red") +
    theme_bw() +
    ylab("accuracy") + 
    xlab("permutation channel") + 
    scale_x_continuous(breaks = c(1:11), labels = c(1:10, "ref"))

内容的提问来源于stack exchange，提问作者user21573410