[R] memory management uestion [Broadcast]

[Liaw, Andy]

I don't see why making copies of the columns you need inside the loop is
"better" memory management.  If the data are in a matrix, accessing
elements is quite fast.  If you're worrying about speed of that, do what
Charles suggest: work with the transpose so that you are accessing
elements in the same column in each iteration of the loop.

Andy 

From: Federico Calboli
> 
> Charles C. Berry wrote:
> 
> > Whoa! You are accessing one ROW at a time.
> > 
> > Either way this will tangle up your cache if you have many rows and 
> > columns in your orignal data.
> > 
> > You might do better to do
> > 
> > Y <- t( X ) ### use '<-' !
> > 
> > for (i in whatever ){
> >     do something using Y[ , i ]
> > }
> 
> My question is NOT how to write the fastest code, it is 
> whether dummy variables (for lack of better words) make the 
> memory management better, i.e. faster, or not.
> 
> Best,
> 
> Fede
> 
> --
> Federico C. F. Calboli
> Department of Epidemiology and Public Health Imperial 
> College, St Mary's Campus Norfolk Place, London W2 1PG
> 
> Tel  +44 (0)20 7594 1602     Fax (+44) 020 7594 3193
> 
> f.calboli [.a.t] imperial.ac.uk
> f.calboli [.a.t] gmail.com
> 
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