R help - Feb 2010 - function on all pairs of vector entries

Hello all, 
Is there a way in R to compute the multivariate normal density of every pair of
entries in a vector efficiently instead of using for loop?
For example 

Suppose I have a vector a=c(v_1,...,v_p)=c(0.5343909, -0.7784353, -0.0568370, 
1.8772838, -1.3183407,  0.8227418,...)
I want to compute density(v_i, v_j) for every pair of entries (i,j) (i!=j) in a.
The joint bivariate distribution is known to be the same for each pair.

Thanks a lot! 
Ivon 
 


 		 	   		  
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try this:

a <- c(0.5343909, -0.7784353, -0.0568370,  1.8772838, -1.3183407, 
0.8227418)
mean <- c(0, 0)
Sigma <- matrix(c(1, 0, 0, 1), 2, 2)

library(mvtnorm)
ind <- combn(length(a), 2)
x <- cbind(a[ind[1, ]], a[ind[2, ]])
dmvnorm(x, mean, Sigma)


I hope it helps.

Best,
Dimitris


On 2/23/2010 8:04 AM, sunivon wrote:
>
>
> Hello all,
> Is there a way in R to compute the multivariate normal density of every
pair of entries in a vector efficiently instead of using for loop?
> For example
>
> Suppose I have a vector a=c(v_1,...,v_p)=c(0.5343909, -0.7784353,
-0.0568370,  1.8772838, -1.3183407,  0.8227418,...)
> I want to compute density(v_i, v_j) for every pair of entries (i,j) (i!=j)
in a.  The joint bivariate distribution is known to be the same for each pair.
>
> Thanks a lot!
> Ivon
>
>
>
>   		 	   		
> _________________________________________________________________
> [[elided Hotmail spam]]
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
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> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
Tel: +31/(0)10/7043478
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