[R] Zero mean correlation Matrix
Charles C. Berry
cberry at tajo.ucsd.edu
Tue Oct 21 18:02:40 CEST 2008
On Mon, 20 Oct 2008, AliR wrote:
>
> Hi,,
>
> I want to use the existing cor function in R but with a different way to
> compute the correlation method.. basically zero mean correlation.
>
> The forumula I have is
>
> 'D' <- function(c1, c2)
> sum(c1*c2, na.rm=T)/(sqrt(sum(c1*c1, na.rm=T))*sqrt(sum(c2*c2, na.rm=T)))
>
>
> I am not sure how i can modify the method cor computes its square roots and
> covariance matrixes? I only need to add this to get the answer
See
?crossprod
If you replace the NA's in c1 and c2 by zeroes, crossprod(c1,c2) is the
same sum(c1*c2) which is the same as sum(c1,c2,na.rm=TRUE) was before you
changed the NAs to zeroes.
HTH,
Chuck
>
>
>
> --
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Charles C. Berry (858) 534-2098
Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901
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