[R] alas, no vecnorm

[Prof Brian D Ripley]

On Thu, 4 May 2000, Faheem Mitha wrote:

> I wanted a function that would give the euclidean distance of a vector. 
> 
> Then I was happy, because I found vecnorm listed on pg 55 of V&R (3rd
> edn) which I had just bought today.

Funny, it is on page 55 of the _second_ edition, and not in the third.
It is the third edition that is R-aware.  Have you really just bought a
second edition?

> Then I was sad, because R did not have vecnorm.
> 
> Then I was happy again, because I bethought myself that I could copy the
> function vecnorm from splus to my code.
> 
> Then I was sad again because R complained
> 
> > vecnorm(v)
> Error in .Fortran("d2norm", as.integer(length(x)), as.double(x), value =
> double(1)) : 
> 	C/Fortran function name not in load table
> 
> So, after this tempest of emotion, the question still remains: does R have
> this function under another name, or was it simply overlooked?

Well, it was not overlooked.  R is not an S-PLUS clone, it is similar to S,
and AFAIK vecnorm is an S-PLUS extension.

vecnorm <- function(x, p=2) sum(x^p)^(1/p)

will do almost all of what vecnorm does, if not as fast as the internal
function, but do you need the speed?  I at least thought vecnorm was not a
priority for R.

-- 
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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