ggplot中使用facet_wrap生成分面图后如何修改图例默认标题

问题原因 #

你当前的图例由aes()中的fill = Depth_bins映射生成，你调用scale_color_discrete修改的是color映射对应的图例，二者相互独立，所以修改不生效，该问题和facet_wrap没有关联。

可行解决方法 #

方法1：通过labs()直接指定（最简便） #

直接在现有labs()参数中添加fill字段，定义fill映射的图例标题，修改后代码如下：

facet_8 <- ggplot(am_dives, aes(x = st_hr, fill = Depth_bins)) +
  geom_density(aes(y = ..count../sum(..count..)), position = "stack", alpha = 0.7) +
  scale_x_datetime(date_labels = "%H:%M") +
  labs(x = "Start hour", y = "Density", fill = "Depth Bins") + # 新增fill参数定义图例标题
  facet_wrap(~ID, dir = "v", scales = "free_y")
facet_8

方法2：修改fill对应的scale参数 #

把你原本写的scale_color_discrete替换为对应fill映射的scale即可：

facet_8 <- ggplot(am_dives, aes(x = st_hr, fill = Depth_bins)) +
  geom_density(aes(y = ..count../sum(..count..)), position = "stack", alpha = 0.7) +
  scale_x_datetime(date_labels = "%H:%M") +
  labs(x = "Start hour", y = "Density") + 
  facet_wrap(~ID, dir = "v", scales = "free_y") + 
  scale_fill_discrete(name = "Depth Bins") # 替换为fill对应的scale修改标题
facet_8

方法3：自定义配色时同步修改标题 #

如果你后续需要自定义深度分箱的颜色、展示标签，也可以在自定义fill scale时同步设置标题，示例如下：

facet_8 <- ggplot(am_dives, aes(x = st_hr, fill = Depth_bins)) +
  geom_density(aes(y = ..count../sum(..count..)), position = "stack", alpha = 0.7) +
  scale_x_datetime(date_labels = "%H:%M") +
  labs(x = "Start hour", y = "Density") + 
  facet_wrap(~ID, dir = "v", scales = "free_y") + 
  scale_fill_manual(
    name = "Depth Bins", # 图例标题
    values = c("#1f77b4", "#ff7f0e", "#2ca02c"), # 自定义颜色，数量和深度分箱数量匹配即可
    labels = c("0-10m", "10-30m", ">30m") # 可选：自定义图例展示标签
  )
facet_8

内容的提问来源于stack exchange，提问作者R student