[Rd] Randomness not due to seed

jeroen00ms jeroen.ooms at stat.ucla.edu
Tue Jul 19 15:13:01 CEST 2011

I am working on a reproducible computing platform for which I would like to
be able to _exactly_ reproduce an R object. However, I am experiencing
unexpected randomness in some calculations. I have a hard time finding out
exactly how it occurs. The code below illustrates the issue. 

mylm1 <- lm(dist~speed, data=cars);
mylm2 <- lm(dist~speed, data=cars);
identical(mylm1, mylm2); #TRUE

makelm <- function(){
	return(lm(dist~speed, data=cars));

mylm1 <- makelm();
mylm2 <- makelm();
identical(mylm1, mylm2); #FALSE

When inspecting both objects there seem to be some rounding differences.
Setting a seed does not make a difference. Is there any way I can remove
this randomness and exactly reproduce the object every time?

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