[R] dist() between groups of data

From: Henrik Parn <henrik.parn_at_bio.ntnu.no>
Date: Fri 24 Feb 2006 - 03:40:19 EST


Dear all,

I have a data set with x and y positions of nests. Each nest can be grouped according to a factor z. I have made a small dummy data set, where the grouping variable z is 0 or 1:

x <- runif(6)
y <- runif(6)
z <- rep(c(0,1), each=3)

xyz <- cbind(x,y,z)
xyz

             x y z
[1,] 0.7176801 0.760944688 0
[2,] 0.2377928 0.080622524 0
[3,] 0.9450770 0.022039470 0
[4,] 0.8725492 0.971996677 1
[5,] 0.6356198 0.001569859 1
[6,] 0.8949670 0.066044377 1

First of all, I suppose that this is the correct way to calculate the Euclidean distance between /all/ nests:

xy <- cbind(x,y)
d.all <- dist(xy)

However, I would like to obtain a distance matrix for distances between nests belonging to certain groups. For example "calculate all distances from nests where z equals something, to nests where z equals something else".

Is it best to split the data in two matrices according to the value of z in the two groups to be compared, and then try to follow the suggestions by Gabor Grothendieck* Date:* Wed 07 Jan 2004 - 15:16:37 EST , or are there other ways that can be applied straight to one matrix?

Thanks in advance!

Henrik

-- 
************************
Henrik Pärn
Department of Biology
NTNU
7491 Trondheim
Norway

+47 735 96282 (office)
+47 909 89 255 (mobile)
+47 735 96100 (fax)

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Received on Fri Feb 24 05:24:26 2006

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