[R] function on all pairs of vector entries

[Dimitris Rizopoulos]

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
>
>
>
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-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

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