将es（x = ...）放入ggplot（）或geom（）之间的区别

Question

What is the difference between putting aes(x=…) in ggplot() or in geom() (eg geom_histogram() below):

1. in ggplot():

ggplot(diamonds) + 
  geom_histogram(binwidth=500, aes(x=diamonds$price))+ 
  xlab("Diamond Price U$") + ylab("Frequency")+ 
  ggtitle("Diamond Price Distribution")

2. in the geom():

ggplot(diamonds, aes(x=diamonds$price)) + 
  geom_histogram(bidwidth= 500) + 
  xlab("Price") + ylab("Frequncy") + 
  ggtitle("Diamonds Price distribution")

Answer 1

Whether you put x = price in the original ggplot() call or in a specific geom only really matters if you have multiple geoms with different mappings. The mapping you specify in the ggplot() call will be applied to all geoms, so it's often best to put the mapping in the top level like that, if only to save you having to type it out again for each individual geom. Specify mappings in the individual geom s if they only apply to that specific geom .

Also note that it should just be aes(x = price) , not aes(x = diamonds$price) . ggplot knows to look in the dataframe you're using as your data argument. If you pass a vector manually like diamonds$price you might mess up facetting or grouping in a more complex plot.