Difference in passing the object inside aes() in ggplot and passing the same object outside ggplot

Question

What is the difference in mapping the Species to color aesthetic inside ggplot and inside geom_point. I am using iris data set.

ggplot(aes(x = Sepal.Length, y = Petal.Length, color = Species), data = 
trainData)+
geom_point()+
geom_smooth()

AND

ggplot(aes(x = Sepal.Length, y = Petal.Length), data = trainData)+
geom_point(aes(color = Species))+
geom_smooth()

The graph I am getting:

Output for the first code

Output for the second code

The geoms inherit all aesthetic mappings which were set in ggplot. — Roland
But why I got -2? I am a beginner in data science and at stack overflow is asking such question wrong here? — Shubham Rajput

Andrew Chisholm Andrew Chisholm · Accepted Answer · 2017-05-12T11:31:06

It's probably because the aes() call in the second case colours the points but this is not carried forward to the colour for the smooth line. Changing the second example to add an explicit call to aes(color...) for the geom_smooth() call results in the same result as the first example.

ggplot(aes(x = Sepal.Length, y = Petal.Length), data = trainData) +
geom_point(aes(color = Species)) +
geom_smooth(aes(color=Species))

Difference in passing the object inside aes() in ggplot and passing the same object outside ggplot

1 Answers