[R] randomness using runif

[Brigid Mooney]

I'm  working on a problem where I'm introducing random error and have
been using the built in function runif to provide that random error.
However, I realized that I seem to be getting some unexpected behavior
out of the function and was hoping someone could share some insight.

I don't know the runif algorithm at all, but from the behavior I'm
seeing, it seems that whenever I open a new R console, the function
runif gets "reset" to some initial value.  For example...

In a NEW R console, enter the following:

x1 <- runif(1000, -1, 1)
x2 <- runif(1000, -1, 1)

x1[1:5]
x2[1:5]

objectsToSave <- c("x1", "x2")
filename <- "C:\\Documents\\x1x2file.Rdata"

save(list=objectsToSave, file=filename, envir = parent.frame())


Then in a different NEW R console, enter this:

x3 <- runif(1000, -1, 1)
x4 <- runif(1000, -1, 1)

x3[1:5]
x4[1:5]
# For me, the values look identical to x1 and x2, but let's check by
loading the x1x2 file and comparing them directly...

filename <- "C:\\Documents\\x1x2file.Rdata"

load(filename)

sum(x1==x3)
sum(x2==x4)


For my results, I get that x1=x3 for all 1000 elements in the vector,
and x2=x4 for all 1000 elements in that vector.

Does anyone have insight into what's going on here?  Am I doing
something wrong here, or is this a quirk of the runif algorithm?  Is
there a better function out there for seeding truly random error?

For what it's worth, here's my R version info:

platform       i386-pc-mingw32
arch           i386
os             mingw32
system         i386, mingw32
status
major          2
minor          8.1
year           2008
month          12
day            22
svn rev        47281
language       R
version.string R version 2.8.1 (2008-12-22)

Thanks for the help,
Brigid