When does the argument go inside or outside aes()?

Question

I am following Chapter 1 of Wickham and Grolemund\'s \"R for data science\" on visualization.

I have tried:

 ggplot(data = mpg) + geom_point(mapping          


        

Answer 1

I remember how completely confused I was by this when I started using ggplot.

To build on @Mauicio Calvao's answer, use color inside the aes to break up the colours in the plot by a variable of data.frame you are plotting eg:

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

So when color (or size or linetype or similar things) is inside the aes it's really asking by what object\variable should the colour groups be determined. If this is a string (eg "blue") then they are all given the one group, but the name of that group isn't related to the actual colour.

To assign colours once grouped by color inside the aes you use scale_color_manual

ggplot(data = mpg) + geom_point(mapping = aes(x = displ, y = hwy, color = drv))+
    scale_colour_manual(values = c("black","blue","orange"))