GGplot scale_fill_discrete 不创建图例

Question

我在之前的 stackoverflow 帖子中使用了该代码，该代码以前使我得到了我想要的带有图例的图形，但是现在我使用的是完全相同的代码，但我的条形图上没有图例。

dput(year.dat2)
structure(list(year = structure(c(1136044800, 1167577200, 1199113200, 
1230735600, 1262275200, 1136044800, 1167577200, 1199113200, 1230735600, 
1262275200, 1136044800, 1167577200, 1199113200, 1230735600, 1262275200
), class = c("POSIXct", "POSIXt"), tzone = ""), variable = structure(c(1L, 
1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L, 3L), .Label = c("SM1", 
"SM2", "SM3"), class = "factor"), value = c(1.24863586758821, 
1.23185757914453, 1.10997352162401, 1.13683917747257, 0.987520605867152, 
2.21498726809749, 1.6378992693761, 1.25635623380691, 1.13585705516765, 
1.10169569342842, 7.40955802109858, 5.7940698875978, 6.03438772314438, 
6.82271157830123, 7.24402375195127)), row.names = c(NA, -15L), .Names = 
c("year", 
"variable", "value"), class = "data.frame")

ggplot(year.dat2, aes(x = year, y = value, fill = factor(variable))) +
  geom_bar(stat = "identity", position = "dodge")+
  scale_fill_discrete(name = "variable",
                      breaks = c(1, 2, 3),
                      labels = c("SM1", "SM2", "SM3")) +
  xlab("year") + 
  ylab("yearly Sub Mean")

结果图：

Answer 1

删除scale_fill_discrete 中的breaks，它们与用作填充aes 的因子variable 数据的值不对应。

这是你想要的代码：

ggplot(year.dat2, aes(x = year, y = value, fill = factor(variable))) +
  geom_bar(stat = "identity", position = "dodge") +
  scale_fill_discrete(name = "variable",
                  labels = c("SM1", "SM2", "SM3")) +
  xlab("year") + 
  ylab("yearly Sub Mean")

注意 1：您甚至不需要 labels 参数，因为您没有重命名 variable 类别。 scale_fill_discrete(name = "variable") 就足够了，或者labs(fill="variable") 是您更改图例标题所需的全部内容。

注意 2：在您的原始帖子中，您链接到了这个 SO 问题：How to get a barplot with several variables side by side grouped by a factor

这里，示例代码scale_fill_discrete(name="Gender", breaks=c(1, 2), labels=c("Male", "Female"))中的breaks实际上引用了原始df中gender的值。同时labels用于将图例中的1重命名为Male，将2重命名为Female。

  Group.1      tea     coke     beer    water gender
1       1 87.70171 27.24834 24.27099 37.24007      1
2       2 24.73330 25.27344 25.64657 24.34669      2

另一方面，您的variable 数据中没有与您在原始代码中设置的breaks 匹配的1,2,3 值，这就是未绘制图例的原因。

为了好玩，这里有一个示例，您可以如何在数据集中使用 breaks 和 labels：

ggplot(year.dat2, aes(x = year, y = value, fill = factor(variable))) +
  geom_bar(stat = "identity", position = "dodge")+
  scale_fill_discrete(name = "variable",
                  breaks = c("SM2", "SM3", "SM1"),
                  labels = c("SM2 new label", "SM3 new label", "SM1 new label")) +
  xlab("year") + 
  ylab("yearly Sub Mean")