[R] fastest way to multiply each column of a matrix by a single vlaue

Philippe Grosjean phgrosje at ulb.ac.be
Tue Sep 4 11:12:29 CEST 2001

```Why not make two versions of your program with each alternative and test
their speed with system.time()? Then, you'll have this indication "in
situation".

Best regards,

Philippe Grosjean

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>Let A be a m by n matrix and b a length n vector. What is the fastest
>vectorized code for doing

>for(j in 1:n) A[, j] <- A[, j]/b[j]   ?

>solution 1:

>t(t(A)/b)

>solution 2:

>B <- matrix( rep(b, m), byrow=T, nrow=m )
>A/B

>anything else?

>I have a program that uses this kind of operation million of times and

>Thanks.

>Jason Liao

=====
Jason G. Liao
Department of Biometry and Epidemiology
Medical University of South Carolina
135 Rutledge Ave., STE 1148, Charleston, SC 29425
phone (843) 876-1114, fax (843) 876-1126

http://www.geocities.com/jg_liao/index.html

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