R: Plotting one ECDF on top of another in different colors

Question

I have a couple of cumulative empirical density functions which I would like to plot on top of each other in order to illustrate differences in the two curves. As was pointed out in a previous question, the function to draw the ECDF is simply plot(Ecdf()) And as I read the fine manual page, I determined that I can plot multiple ECDFs on top of each other using something like the following:

require( Hmisc )
set.seed(3)
g <- c(rep(1, 20), rep(2, 20))  
Ecdf(c( rnorm(20), rnorm(20)), group=g)

However my curves sometimes overlap a bit and can be hard to tell which is which, just like the example above which produces this graph:

enter image description here

I would really like to make the color of these two CDFs different. I can't figure out how to do that, however. Any tips?

Time to switch from Guiness back to coffee, JD. There is a `col=` argument, see my edited answer. — Dirk Eddelbuettel, Jun 14 '11 at 13:29

Dirk Eddelbuettel · Accepted Answer · 2011-06-14T13:29:11.910

13

If memory serves, I have done this in the past. As I recall, you needed to trick it as Ecdf() is so darn paramterised. I think in help(ecdf) it hints that it is just a plot of stepfunctions, so you could estimate two or more ecdfs, plot one and then annotate via lines().

Edit Turns out it is as easy as

  R> Ecdf(c(rnorm(20), rnorm(20)), group=g, col=c('blue', 'orange'))

as the help page clearly states the col= argument. But I have also found some scriptlets where I used plot.stepfun() explicitly.

edited Jun 14 '11 at 13:29

answered Jun 14 '11 at 13:20

Dirk Eddelbuettel

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It is CLEARLY stated in the manuals, which I thought I read. Obviously my glass of Guinness was blocking that part of the screen. – JD Long Jun 14 '11 at 13:40
Wow, they do 64oz 'gulp' glasses now? – Dirk Eddelbuettel Jun 14 '11 at 17:01
When I landed in DUB they hooked me to an IV bag of Guinness. It was the IV bag blocking my screen. – JD Long Jun 15 '11 at 16:18

score 7 · Answer 2 · answered Jun 14 '11 at 13:31

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You can add each curve one at a time (each with its own style), e.g.

Ecdf(rnorm(20), lwd = 2)
Ecdf(rnorm(20),add = TRUE, col = 'red', lty = 1)

answered Jun 14 '11 at 13:31

nullglob

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You can do it one operation too as `col`, `lty`, ... are all vectorised. – Dirk Eddelbuettel Jun 14 '11 at 13:34

score 0 · Answer 3 · answered Mar 09 '20 at 06:39

0

Without using Ecdf (doesn't look like Hmisc is available):

set.seed(3)
mat <- cbind(rnorm(20), rnorm(20))
matplot(apply(mat, 2, sort), seq(20)/20, type='s')

answered Mar 09 '20 at 06:39

algae

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R: Plotting one ECDF on top of another in different colors

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