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

[Jason Liao]

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
I appreciate your input.

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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