set.seed ( ) function

Hi Josh,

Thanks for your reply.

The problem is have is in trying to retain the proportions of 2 groups in my
data while sampling into training and test sets. I find that different
?arguments for set.seed give very different proportions of my 2 groups in
the training and test sets.

Penny.



On 22/04/2011 3:27 p.m., Joshua Wiley wrote:

Hi,

On Thu, Apr 21, 2011 at 8:18 PM, Penny Bilton<pennybilton at xnet.co.nz>
?wrote:

I am using /set.seed()/ ? before the /sample/ ? function.

How does the length of the argument of /set.seed()/ ? and order of the
digits affect how the sampling is carried out?

You can use set.seed() to specify a particular seed so that while
pseudo-random numbers are sampled, you can repeat it. ?For example:

set.seed(10)
rnorm(10)
set.seed(10)
rnorm(10)

Specifically, I have used set.seed(123456789). Will this configuration
give me a genuinely random sampling??

You will never get truly random sampling from a computer algorithm,
but it is darn close and more than adequate in the majority of cases.
123456789 is just a length 1 vector containing the number 123456789,
not 9 separate numbers.

Google will be able to give you a lot of information on pseudo-random
number algorithms as well as the concept of "seeds". ?Also see
?set.seed

Cheers,

Josh

Thank you in anticipation.

Penny.


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