[R] vectorization of groups of dot products

From: Rossi, Peter E. <Peter.Rossi_at_chicagogsb.edu>
Date: Sat 07 Jan 2006 - 08:56:25 EST

 

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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