Highlighting grouped data points by size and symbol type

Sometimes we may not want to use different colors to represent different groups of data points. For example, some journals accept graphs only in grayscale. In this recipe, we will see how we can highlight grouped data points by symbol size and type.

Getting ready

We will use the ggplot2 library, so let's load it by running the following command:

library(ggplot2)

How to do it...

First, let's group points by symbol type. Once again we use the qplot() function:

qplot(disp,mpg,data=mtcars,shape=as.factor(cyl)) 
How to do it...

Next, let's group the points simply by the size of the plotting symbol:

qplot(disp,mpg,data=mtcars,size=as.factor(cyl))
How to do it...

How it works...

Highlighting groups of points by symbol type and size works exactly like color using the qplot() functions. Instead of the col argument, we used the shape and size arguments and set them to the factor we want to group the points by (in this case cyl). We can also use combinations of any of these arguments. For example, we could use color to represent cyl and size to represent gear.

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