在ggplot2（R语言）中调整色条图例的显示范围

• 需求：展示Observation变量随时间的变化趋势，使用指定配色为数据点着色；希望仅限制色条图例的显示区间（如-10到100），提升小值区间的颜色区分度，同时不改变原有数据点的颜色映射规则。
• 当前问题：代码可正常运行，但色条图例因包含0-1000的大范围，小值区域颜色区分度极低，视觉效果差。
• 用户原代码：

# 定义颜色刻度
colors <- c("black", "grey", "darkred", "red", "tomato", "white", "white",
            "lightgreen", "green", "darkgreen", "darkolivegreen", 
            "cyan", "blue", "darkblue", "midnightblue", "purple", 
            "magenta", "darkmagenta", "yellow", "gold4")
values <- c(-10, -5, -3, -1.5, -0.001, 0, 0.001, 4, 6, 8, 10, 15, 20, 40, 60, 80, 100, 200, 500, 1000)

# 绘图
ggplot(notes2023, aes(x = Date, y = Observations)) +
  geom_point(aes(colour = Observations), size = 1) +
  scale_color_gradientn(colours = colors, values = scales::rescale(values), limits = c(-10, 1000),
                        oob = scales::squish, name = 'Indice', 
                        guide = guide_colorbar(direction = "vertical", barwidth = 1, barheight = 10, limits = c(-10, 100), title.position = "top")) +
  geom_smooth(color = "black", span = 0.2, size = 0.5) +
  scale_y_continuous(trans = pseudolog10_trans, breaks = c(-5, 0, 5, 10, 20, 50, 100, 1000)) +
  labs(title = "Observations journalières", subtitle = "2023", x = "Date", y = "Observation") +
  theme_clean(base_size = 5) +
  theme(legend.title.align = 0.5, legend.text = element_text(size = 6))

• 当前图表效果：色条大部分区域被高值（100-1000）占据，-10到100区间的颜色压缩在极小范围内，无法清晰区分小值对应的颜色。

核心思路：保持数据点的颜色映射规则（基于-10到1000的范围）不变，仅通过guide_colorbar的参数调整色条的显示区间、刻度密度，提升小值区域的视觉区分度。

修改后的代码：

# 定义颜色刻度
colors <- c("black", "grey", "darkred", "red", "tomato", "white", "white",
            "lightgreen", "green", "darkgreen", "darkolivegreen", 
            "cyan", "blue", "darkblue", "midnightblue", "purple", 
            "magenta", "darkmagenta", "yellow", "gold4")
values <- c(-10, -5, -3, -1.5, -0.001, 0, 0.001, 4, 6, 8, 10, 15, 20, 40, 60, 80, 100, 200, 500, 1000)

# 绘图
ggplot(notes2023, aes(x = Date, y = Observations)) +
  geom_point(aes(colour = Observations), size = 1) +
  scale_color_gradientn(
    colours = colors, 
    values = scales::rescale(values), 
    limits = c(-10, 1000),  # 保持原有颜色映射范围
    oob = scales::squish,    # 超出范围的值压缩到边界颜色
    name = 'Indice', 
    guide = guide_colorbar(
      direction = "vertical", 
      barwidth = 1, 
      barheight = 10, 
      limits = c(-10, 100),  # 色条仅显示-10到100区间
      breaks = c(-10, -5, -3, -1.5, 0, 4, 6, 8, 10, 15, 20, 40, 60, 80, 100),  # 增加小值刻度，提升区分度
      labels = c(-10, -5, -3, -1.5, 0, 4, 6, 8, 10, 15, 20, 40, 60, 80, "≥100"),  # 标注高值压缩提示
      title.position = "top"
    )
  ) +
  geom_smooth(color = "black", span = 0.2, size = 0.5) +
  scale_y_continuous(trans = pseudolog10_trans, breaks = c(-5, 0, 5, 10, 20, 50, 100, 1000)) +
  labs(title = "Observations journalières", subtitle = "2023", x = "Date", y = "Observation") +
  theme_clean(base_size = 5) +
  theme(legend.title.align = 0.5, legend.text = element_text(size = 6))

• 保留scale_color_gradientn的limits = c(-10, 1000)和oob = scales::squish，确保数据点的颜色映射规则不变（≥100的点统一使用gold4颜色）。
• 在guide_colorbar中：
  • 设置limits = c(-10, 100)，让色条仅展示小值区间。
  • 增加breaks参数，添加更多小值刻度，让颜色变化更清晰。
  • 修改labels，将100标注为≥100，直观提示用户高值已被压缩到该颜色。

内容的提问来源于Stack Exchange，提问作者Constantin Marguier