On Thu, 30 Sep 1999, Stephen R. Laniel wrote:
On 10/1/99, 9:42 AM +1000, Michael HART wrote:
I have a number of items with "distances" of differences between each other. What I want to do is to plot each item on a two dimensional plot such that the positions on the plot indicate the approximate distance between each item.
This doesn't seem like an especially R-related question, but I'll take a stab at it anyway. To plot these distances, won't you need to resolve their positions first? To resolve their positions, you could use a whole lot of methods (there's a seminal paper by Householder whose title I can't remember now -- it's a little paper, but dense). The important thing to note is that a collection of distances doesn't uniquely specify a configuration; if I'm not mistaken, it only specifies configurations up to rigid motion. You need to fix a coordinate system and define one of the points as an origin.
Yes, and also up to reflections.
In any event, the whole problem seems beyond the scope of this list, unless I'm mistaken.
This problem is usually known as multidimensional scaling, I think because influence of psychometricians. There is an R function cmdscale in package mva for `classical' MDS, where the distances really are Euclidean distances, and functions sammon and isoMDS (to which it refers) for other `distances' are in package MASS in the VR6 bundle on CRAN. You will find a description of this in most Multivariate Analysis texts, and in Venables & Ripley.
Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272860 (secr) Oxford OX1 3TG, UK Fax: +44 1865 272595 -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._