[R] question from Braun/Murdoch book

[Prof Brian Ripley]

On Wed, 8 Oct 2008, Erin Hodgess wrote:

> Hi R People:
>
> I am looking at the Braun/Murdoch book, " A First Course in
> Statistical Programming in R", and I have a question about a function
> there.  It's on page 52, Example 4.5; the sieve of Erastosthenes.
>
> There is a line:
> primes <- c()
>
> Is there a difference between using that and
> primes <- NULL
> please?
>
> When you put in primes <- c(), primes comes back as NULL.
>
>
> Is one more efficient or is this just a matter of programming style, please?

What would be more efficient is primes <- integer(0) (as it looks like 
'primes' concatenates integer vectors, at a quick glance).

Use a function call c() to get NULL is not efficient, but all the 
differences here are tiny.

> Thanks in advance,
> Sincerely,
> Erin
>
>
> -- 
> Erin Hodgess
> Associate Professor
> Department of Computer and Mathematical Sciences
> University of Houston - Downtown
> mailto: erinm.hodgess at gmail.com
>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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