How to create a density plot for data from multiple years with each year represented by a different colour?

Question

I have data on a variable spanning multiple years.

I want to see how the distribution has evolved over the years.

• Is there an easy way to produce a density plot for each year in single plot with different colours for each year?

Answer 1

Without seeing the data, I would suggest trying trellis displays. If you are using R, this is very easy to do with the lattice (even latticeExtra) or ggplot2 packages.

> my.df <- data.frame(x=rnorm(300), year=gl(3, 100, 300, labels=2000:2002))
> head(my.df)
           x year
1 -0.3260365 2000
2  0.5524619 2000
3 -0.6749438 2000
4  0.2143595 2000
5  0.3107692 2000
6  1.1739663 2000
> library(lattice)
> densityplot(~ x, data=my.df, groups=year)

which gives

Compare to densityplot(~ x | year, data=my.df, layout=c(3,1)) (for a facetted display).

Answer 2

I'll assume you are using R (from previous questions). Note that this also makes your question better suited for StackOverflow.com.

As such, I remembered an answer there that could be of service to you:Q6030684.