在ggplot

Question

首先，我运行此代码并且它完美运行（所有数据点都变为蓝色）：

ggplot(data = mpg) + geom_point(mapping = aes(x = displ, y = hwy), color = "blue")

但是当我尝试移动下面的映射时，数据点变为黑色而不是蓝色。

为什么？

ggplot(data = mpg, mapping = aes(x = displ, y = hwy), color = "blue") + geom_point() 

Answer 1

您可以在几何之间的映射内共享变量。特别是关于color，当设置为常量（例如aes）而不是变量（在此处说明时），需要在geom外部和"blue"中进行定义。 Answer to: When does the argument go inside or outside aes。

我在下面提供了一些示例，以更好地说明这一点；

library(ggplot2)

## works fine for each geom 
ggplot(data = mpg, aes(x = displ, y = hwy)) + 
  geom_point(color = "blue") + 
  geom_line(color="red")

## doesn't work when not in the geom
ggplot(data = mpg, aes(x = displ, y = hwy), color = "blue") + 
  geom_point() 

## gets evaluated as a variable when in aes
ggplot(data = mpg, aes(x = displ, y = hwy)) + 
  geom_point(aes(color = "blue")) 

## can use a variable in aes, either in geom or ggplot function
ggplot(data = mpg, aes(x = displ, y = hwy)) + 
  geom_point(aes(color = model), show.legend = FALSE)