I've been getting up to speed with R in the last month.

Here is my question:

What is a good way to assign colors to categorical variables in ggplot2 that have stable mapping? I need consistent colors across a set of graphs that have different subsets and a different number of categorical variables.

For example,

plot1 <- ggplot(data, aes(xData, yData,color=categoricaldData)) + geom_line()

where **categoricalData **has 5 levels.

And then

plot2 <- ggplot(data.subset, aes(xData.subset, yData.subset,

color=categoricaldData.subset)) + geom_line()

where categoricalData.subset has 3 levels.

However, a particular level that is in both sets will end up with a different color, which makes it harder to read the graphs together.

Do I need to create a vector of colors in the data frame? Or is there another way to assigns specific colors to categories?