[R] Creating 3 vectors that sum to 1

[Ravi Varadhan]

The following one-liner generates uniformly distributed 3-tuples that sum to 1:

diff(c(0, sort(runif(2)), 1))

More, generally you can generate n-tuples that sum to unity as:

diff(c(0, sort(runif(n-1)), 1))


Ravi.

____________________________________________________________________

Ravi Varadhan, Ph.D.
Assistant Professor,
Division of Geriatric Medicine and Gerontology
School of Medicine
Johns Hopkins University

Ph. (410) 502-2619
email: rvaradhan at jhmi.edu


----- Original Message -----
From: Greg Snow <Greg.Snow at imail.org>
Date: Tuesday, March 29, 2011 1:02 pm
Subject: Re: [R] Creating 3 vectors that sum to 1
To: Christopher Desjardins <cddesjardins at gmail.com>, "r-help at r-project.org" <r-help at r-project.org>


> Do a search for Dirichlet, that may give you the tools you need.  Also 
> for plotting 3 vectors that sum to 1, instead of a 3d scatter plot you 
> should look into a triangle or trilinear plot, see ?triplot in the 
> TeachingDemos package (the see also for that help page lists several 
> other implementations in other packages as well).
> 
> -- 
> Gregory (Greg) L. Snow Ph.D.
> Statistical Data Center
> Intermountain Healthcare
> greg.snow at imail.org
> 801.408.8111
> 
> 
> > -----Original Message-----
> > From: r-help-bounces at r-project.org [
> > project.org] On Behalf Of Christopher Desjardins
> > Sent: Tuesday, March 29, 2011 10:20 AM
> > To: r-help at r-project.org
> > Subject: [R] Creating 3 vectors that sum to 1
> > 
> > I have 3 vectors: p1, p2, and p3. I would like each vector to be any
> > possible value between 0 and 1 and p1 + p2 + p3 = 1. I want to graph
> > these
> > and I've thought about using scatterplot3d(). Here's what I have so
> > far.
> > 
> > library(scatterplot3d)
> > p1 <- c(1,0,0,.5,.5,0,.5,.25,.25,.34,.33,.33,.8,.1,.1,.9,.05,.05)
> > p2 <- c(0,1,0,.5,0,.5,.25,.5,.25,.33,.34,.33,.1,.8,.1,.05,.9,.05)
> > p3 <- c(0,0,1,0,.5,.5,.25,.25,.5,.33,.33,.34,.1,.1,.8,.05,.05,.9)
> > scatterplot3d(p1,p2,p3)
> > 
> > 
> > However, I wonder if there is an easy way to create vectors p1, p2, 
> and
> > p3.
> > 
> > 	[[alternative HTML version deleted]]
> > 
> > ______________________________________________
> > R-help at r-project.org mailing list
> > 
> > PLEASE do read the posting guide 
> > guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> 
> ______________________________________________
> R-help at r-project.org mailing list
> 
> PLEASE do read the posting guide 
> and provide commented, minimal, self-contained, reproducible code.