[R] Avoiding for-loops

[roger koenker]

lower triangle can be obtained by

	A[row(A)>col(A)]

url:	www.econ.uiuc.edu/~roger        	Roger Koenker
email	rkoenker at uiuc.edu			Department of Economics
vox: 	217-333-4558				University of Illinois
fax:   	217-244-6678				Champaign, IL 61820

On Nov 25, 2004, at 11:15 AM, John wrote:

> Hello R-users,
>
> I have a symmetric matrix of numerical values and I
> want to obtain those values in the upper or lower
> triangle of the matrix in a vector. I tried to do the
> job by using two for-loops but it doens't seem to be a
> clever way, and I'd like to know a more efficient code
> for a large matrix of thousands of rows and columns.
> Below is my code for your reference.
>
> Thanks a lot.
>
> John
>
> ####################
>
> # mtx.sym is a symmetric matrix
>
>> my.ftn <- function(size_mtx, mtx) {
> + my.vector <- c()
> + for ( i in 1:size_mtx ) {
> + cat(".")
> + for ( j in 1:size_mtx ) {
> + if ( upper.tri(mtx)[i,j] ) {
> + my.vector <- c(my.vector, mtx[i,j])
> + }}}
> + cat("\n")
> + }
>>
> # if I have a matrix, mtx.sym, of 100x100
>> my.ftn(100, mtx.sym)
>
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