[R] recycling rule

[Prof Brian D Ripley]

On Tue, 23 Nov 1999, Thomas Lumley wrote:

> On Wed, 24 Nov 1999, Research Division wrote:
> 
> > I was illustrating the use of R to some of my students 
> > here in the Philippines: 
> > The following question was posed:  "is there any 
> > motivation for the development
> > of the recycling rule for vector 
> > manipulation, especially for fractional replication?"
> > I had no idea how to answer this. 
> 
> For integer replication I think the motivation is to handle
> vector+scalar, vector+matrix, and scalar+matrix operations.

I think it is buried in the mists of time, but apart from these there
are efficiency shortcuts for other common operations where a scalar
needs to be expanded to a vector, e.g. in the args to rnorm.

> I would say that the fractional replication is just a side-effect.

Possibly even originally unintentional. It is not allowed in current
versions of S (S, not necessarily S-PLUS) and should probably be
discouraged.

-- 
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)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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