ggplot双Y轴图表线条图例添加问题求助

问题说明 #

使用ggplot绘制双Y轴图表时，次Y轴（Z/E ratio）对应的线条无法显示图例。

数据 #

> dput(figure4)
structure(list(Days = c(1.3, 3, 4, 6, 7.7, 1, 4, 7.7, 1, 4, 6, 
7.7), type = c("Indirect", "Indirect", "Indirect", "Indirect", 
"Indirect", "Direct_control", "Direct_control", "Direct_control", 
"Temp_control", "Temp_control", "Temp_control", "Temp_control"
), fraction = c(100, 75.9, 63.8, 39.2, 32.4, 100, 96.35, 98.1, 
100, 107.05, 102.45, 96.26), ratio2 = c(2.87, 2.86, 2.94, 3.55, 
3.8, 3.99, 3.638, 4.189, 1.088, 1.112, 1.07, 1.12), se2 = c(15, 
11.38, 9.57, 5.88, 4.86, 15, 14.88, 14.7, 15, 16.0571, 15.368, 
14.439)), class = c("tbl_df", "tbl", "data.frame"), row.names = c(NA, 
-12L))

当前图表 #

当前代码 #

ylim.prim <- c(0, 120)   # 百分比
ylim.sec <- c(0, 5)    # 比值
b <- diff(ylim.prim)/diff(ylim.sec)
a <- ylim.prim[1] - b*ylim.sec[1]
ggplot(figure4, aes(x=Days, y=fraction, shape = type, colour = type)) +
  geom_point(size=4) +
  geom_errorbar(aes(ymax = fraction + se2, ymin = fraction - se2, group= type),  width = 0.25)+
  geom_line(aes(x=Days, y=a + ratio2*b,colour = type, linetype = Ratio), size= 1)+
  scale_y_continuous("Fraction remainig(%)", sec.axis = sec_axis(~ (. - a)/b, name = "Z/E ratio"))+ theme(text = element_text(size = 15))+ 
  theme(axis.text.x = element_text(angle = 0, vjust = 1, hjust= 1,size =12 ))+
  theme(axis.text.y = element_text(size =12 ))+
   theme(text = element_text(size = 15)) +
  theme(panel.grid.major = element_blank(), panel.grid.minor = element_blank(),
        panel.background = element_blank(), axis.line = element_line(colour = "black"))

解决建议 #

问题根源 #

代码中geom_line的linetype = Ratio是无效映射——你的数据里没有名为Ratio的列，ggplot无法识别这个变量，自然不会生成对应的图例。另外，要让次Y轴的线条图例和主Y轴的点图例协同显示，需要调整映射逻辑。

修正后的代码方案 #

这里提供两种常见的处理方式：

方式1：给线条指定固定线型，合并图例

如果希望线条和点共用type的图例，只需移除无效的linetype = Ratio，确保线条的colour映射到type，这样ggplot会自动合并点和线条的图例：

ylim.prim <- c(0, 120)   # 百分比
ylim.sec <- c(0, 5)    # 比值
b <- diff(ylim.prim)/diff(ylim.sec)
a <- ylim.prim[1] - b*ylim.sec[1]

ggplot(figure4, aes(x=Days, colour = type)) +
  # 主Y轴的点和误差棒
  geom_point(aes(y=fraction, shape = type), size=4) +
  geom_errorbar(aes(y=fraction, ymax = fraction + se2, ymin = fraction - se2, group= type), width = 0.25)+
  # 次Y轴的线条
  geom_line(aes(y=a + ratio2*b), size= 1)+
  scale_y_continuous("Fraction remaining(%)", sec.axis = sec_axis(~ (. - a)/b, name = "Z/E ratio"))+
  # 统一主题设置（合并重复的theme）
  theme(text = element_text(size = 15),
        axis.text.x = element_text(angle = 0, vjust = 1, hjust= 1,size =12 ),
        axis.text.y = element_text(size =12 ),
        panel.grid.major = element_blank(), 
        panel.grid.minor = element_blank(),
        panel.background = element_blank(), 
        axis.line = element_line(colour = "black"))

方式2：单独为线条创建图例（区分点和线）

如果希望单独显示线条对应的图例（标注为Z/E ratio），可以手动设置linetype的固定值并添加对应的scale：

ylim.prim <- c(0, 120)   # 百分比
ylim.sec <- c(0, 5)    # 比值
b <- diff(ylim.prim)/diff(ylim.sec)
a <- ylim.prim[1] - b*ylim.sec[1]

ggplot(figure4, aes(x=Days)) +
  # 主Y轴的点和误差棒
  geom_point(aes(y=fraction, shape = type, colour = type), size=4) +
  geom_errorbar(aes(y=fraction, ymax = fraction + se2, ymin = fraction - se2, group= type, colour = type), width = 0.25)+
  # 次Y轴的线条，指定linetype为1（实线），并映射到固定字符串
  geom_line(aes(y=a + ratio2*b, colour = type, linetype = "Z/E ratio"), size= 1)+
  scale_y_continuous("Fraction remaining(%)", sec.axis = sec_axis(~ (. - a)/b, name = "Z/E ratio"))+
  # 设置线型图例
  scale_linetype_manual(values = 1, name = "")+
  # 主题设置
  theme(text = element_text(size = 15),
        axis.text.x = element_text(angle = 0, vjust = 1, hjust= 1,size =12 ),
        axis.text.y = element_text(size =12 ),
        panel.grid.major = element_blank(), 
        panel.grid.minor = element_blank(),
        panel.background = element_blank(), 
        axis.line = element_line(colour = "black"))

额外优化点 #

• 代码里的Fraction remainig拼写错误，修正为Fraction remaining
• 合并重复的theme(text = element_text(size = 15))设置，让代码更简洁

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