[R] how much performance penalty does this incur, scalar as a vector of one element?
Luke Tierney
luke at stat.uiowa.edu
Thu Feb 22 15:36:27 CET 2007
I think the short answer is not much.
Longer answer: In an interpreted framework with double precision
floating point scalars there is little chance of avoiding fresh
allocations for each scalar; given that, the overhead associated with
length checks can be made negligible. (That isn't to say it currently
is--it may or may not be, but you asked about design.) Systems that
support integer scalars often represent them as immediate values within
pointers by sacrificing one or two bits of precision in the integers,
but that doesn't work for double precision floats except possibly on
64-bit systems. Though even there it would be possible to use an
efficient internal representation of vectors of length one without
changing the concept that everything is a vector.
As we think about compilation there are opportunities to produce more
efficient code if values can be assumed to be scalars, but that can be
accomplished by adding a declaration mechanism. So again the answer
in terms of efficiency cost is not much.
The APL view of everything as an array, with zero-dimensional arrays
being scalars and higher-dimensional arrays being real entities rather
than decorated vectors, is in many ways conceptually cleaner and might
in hindsight have been a better choice for that reason, but efficiency
isn't really a consideration.
Best,
luke
On Wed, 21 Feb 2007, Jason Liao wrote:
>
> I have been comparing R with other languages and systems. One peculiar feature of R is there is no scalar. Instead, it is just a vector of length one. I wondered how much performance penalty this deign cause, particular in situations with many scalars in a program. Thanks.
>
>
>
> Jason Liao, http://www.geocities.com/jg_liao
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--
Luke Tierney
Chair, Statistics and Actuarial Science
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa Phone: 319-335-3386
Department of Statistics and Fax: 319-335-3017
Actuarial Science
241 Schaeffer Hall email: luke at stat.uiowa.edu
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