R语言ggplot2绘制双Y轴图表遇轴刻度问题求助

我需要绘制一张目标图样式的双Y轴图表，但目前轴刻度显示异常，多次修改代码后仍不符合预期。以下是我的数据和代码，请帮忙解决刻度不匹配的问题：

# Datos Clorofila-Radiación
horario <- c("D1-6:30", "D1-12:00", "D1-18:00", "D2-6:30", "D2-12:00", "D2-18:00", "D3-        6:30", "D3-12:00", "D3-18:00")
trh3 <- c(1.85, 1.21, 2.23, 1.50, 1.11, 1.86, 1.74, 1.2, 1.63)
trh5 <- c(1.99, 1.50, 1.98, 1.90, 1.14, 2.01, 1.59, 1.04, 1.53)
rad <- c(22.53, 1909.10, 30.32, 22.32, 2342.10, 12.65, 28.70, 1279.8, 28.68)

# Crear un data frame
datos <- data.frame(horario, trh3, trh5, rad)

# Ordenar los datos por el orden deseado en el eje x
datos$horario <- factor(datos$horario, levels = c("D1-6:30","D1-12:00","D1-18:00","D2-6:30","D2-12:00","D2-18:00","D3-6:30","D3-12:00","D3-18:00"))

# Gráfico
ggplot(datos, aes(x = horario)) +
   geom_line(aes(y = trh3, color = "trh3", group = 1)) +
   geom_line(aes(y = trh5, color = "trh5", group = 1)) +
   geom_line(aes(y = rad, color = "rad", group = 1), linetype = "dashed") +
   scale_y_continuous(
     name = "Clorofila (µg/ml)",
     breaks = seq(1, 2.5, by = 0.2),
     labels = seq(1, 2.5, by = 0.2)) +
   scale_y_continuous(
     sec.axis = sec_axis(~./1000, name = "Radiación solar (W/m²)", breaks = seq(0, 2500, by = 500)/1000),
     name = "Radiación solar (W/m²)",
     breaks = seq(0, 2500, by = 500),
     labels = seq(0, 2500, by = 500)) +
   scale_color_manual(
     values = c("trh3" = "blue", "trh5" = "green", "rad" = "red"),
     labels = c("trh3 (Clorofila)" = "trh3", "trh5 (Clorofila)" = "trh5", "Radiación solar")) +
   labs(x = "Semana de medición", y = "Parámetros", color = "Variable") +
   theme_minimal() +
   theme(legend.position = "bottom")

问题根源分析 #

你的代码存在3个核心问题导致刻度异常：

• 重复调用scale_y_continuous，第二个调用会完全覆盖第一个的左轴设置，导致叶绿素的刻度失效
• 辐射数据rad的数值范围（20-2300）远大于叶绿素数据（1-2.5），直接绘制会压缩叶绿素线条，双Y轴的核心逻辑是先将右轴数据转换到左轴范围，再通过反向转换显示原始刻度
• scale_color_manual的标签映射搞反了，键值对位置错误

修正后的完整代码 #

# Datos Clorofila-Radiación
horario <- c("D1-6:30", "D1-12:00", "D1-18:00", "D2-6:30", "D2-12:00", "D2-18:00", "D3-6:30", "D3-12:00", "D3-18:00")
trh3 <- c(1.85, 1.21, 2.23, 1.50, 1.11, 1.86, 1.74, 1.2, 1.63)
trh5 <- c(1.99, 1.50, 1.98, 1.90, 1.14, 2.01, 1.59, 1.04, 1.53)
rad <- c(22.53, 1909.10, 30.32, 22.32, 2342.10, 12.65, 28.70, 1279.8, 28.68)

# Crear un data frame
datos <- data.frame(horario, trh3, trh5, rad)

# Ordenar los datos por el orden deseado en el eje x
datos$horario <- factor(datos$horario, levels = c("D1-6:30","D1-12:00","D1-18:00","D2-6:30","D2-12:00","D2-18:00","D3-6:30","D3-12:00","D3-18:00"))

# Gráfico修正版
ggplot(datos, aes(x = horario)) +
  # 叶绿素数据直接使用原始值
  geom_line(aes(y = trh3, color = "trh3", group = 1)) +
  geom_line(aes(y = trh5, color = "trh5", group = 1)) +
  # 将辐射数据转换为左轴匹配范围（除以1000）
  geom_line(aes(y = rad/1000, color = "rad", group = 1), linetype = "dashed") +
  # 统一设置Y轴：左轴为叶绿素，右轴通过反向转换还原辐射刻度
  scale_y_continuous(
    name = "Clorofila (µg/ml)",
    breaks = seq(1, 2.5, by = 0.2),
    labels = seq(1, 2.5, by = 0.2),
    sec.axis = sec_axis(~.*1000, name = "Radiación solar (W/m²)", breaks = seq(0, 2500, by = 500))
  ) +
  # 修正颜色标签映射
  scale_color_manual(
    values = c("trh3" = "blue", "trh5" = "green", "rad" = "red"),
    labels = c("trh3 (Clorofila)", "trh5 (Clorofila)", "Radiación solar")
  ) +
  labs(x = "Semana de medición", color = "Variable") +
  theme_minimal() +
  theme(legend.position = "bottom")

关键修改说明 #

1. 合并Y轴设置：只调用一次scale_y_continuous，避免左轴设置被覆盖，同时在同一个函数内定义右轴的反向转换规则
2. 数据范围对齐：将rad除以1000，让其数值范围（0.01-2.3）与叶绿素数据（1-2.5）匹配，保证三条曲线都能正常显示
3. 右轴刻度还原：sec_axis(~.*1000)将左轴刻度值乘以1000，还原辐射数据的原始单位（W/m²），同时设置符合需求的刻度断点
4. 修正颜色标签：调整scale_color_manual的labels参数，让标签文本与颜色值正确对应

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