[R] vectorization of groups of dot products

[Berton Gunter]

colSums(X^2) -- or am I missing something?

-- Bert Gunter
Genentech Non-Clinical Statistics
South San Francisco, CA
 
"The business of the statistician is to catalyze the scientific learning
process."  - George E. P. Box
 
 

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch 
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Rossi, Peter E.
> Sent: Friday, January 06, 2006 1:56 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] vectorization of groups of dot products
> 
>  
> I have a set of n vectors, x_1, ..., x_n, of the same length.
> I would like to form the vector of dot products -- x_1'x_1, 
> ..., x_n'x_n
> 
> the fastest way I can think to do this is to put the vectors into a
> matrix
> and do 
> 
> diag(crossprod(X))
> 
> however, this seems to be very wasteful since this computes n(n+1)/2-n
> unnecessary
> dot products.
> 
> Is there a better way using existing functions in R?
> 
> thanks!
> 
> peter
> 
> 
> ................................
>   Peter E. Rossi
>  Joseph T. and Bernice S. Lewis Professor of Marketing and Statistics
>  Editor, Quantitative Marketing and Economics
>  Rm 353, Graduate School of Business, U of Chicago
>  5807 S. Woodlawn Ave, Chicago IL 60637, USA
>  Tel: (773) 702-7513   |   Fax: (773) 834-2081
> 
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