What is the order of groups in plot.survfit used for color or line types?

Question

I am writing a script that will generate plots of plot(survfit(Surv(time, event)~factor)).

The different survival curves will have a different color. How is the order of the color defined? is it levels(factor)? unique(factor)?

My point is that I would like to automatically script the legend labels and text. Can I safely I use levels(factor) as legend text?

I am sure this is documented somewhere but the help entry of ?plot.survfit is not very helpful?

Answer 1

Yes, the order of the color depends on levels(factor), and yes, you can use levels(factor) for your legend text.

This applies everytime you are dealing with a factor. There is also a number of functions for you to manipulate the levels of your factor if you need so, e.g. check ?relevel.