R devel - Feb 2008 - a != a*1 != a+0 != +a

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Hi

I am writing a package for multivariate polynomials ('multipols')
using S3 methods.

The package includes a Ops.multipol()  function for the
arithmetic methods;  I would like
to define some sort of user-specified Boolean option which, if
set,  would force results to be simplified as they are produced.

Call this option "trim".  Trimming a multipol results in
a smaller array that is more manageable.

Mostly one wants to trim, sometimes not.


Would options() be a good way to manage this?

One issue is the behaviour of unary operators "+" and "-".

If trim is TRUE, then  "a"   is one thing,  but "+a" 
returns
"trim(a)", which might be different.

Also "1*a" would be different from "a" and "a+0"



Does the List consider this to be Good Practice?

Has anyone got comments?



--
Robin Hankin
Uncertainty Analyst and Neutral Theorist,
National Oceanography Centre, Southampton
European Way, Southampton SO14 3ZH, UK
  tel  023-8059-7743

I don't think global options are desirable.

I would make your operators work in a single way and if the user
wants a different way he can call whatever functions you provide
directly instead of using the operators.

If you really need two ways with operators I would define a subclass
with operators working in the alternative way and have as.whatever
methods that converts back and forth.

Another possibility is to have the way it works be a special
attribute of the object itself (other than "class").

On Feb 4, 2008 9:25 AM, Robin Hankin <r.hankin at noc.soton.ac.uk>
wrote:
> hits=1.0 tests=MANY_EXCLAMATIONS
> X-USF-Spam-Flag: NO
>
> Hi
>
> I am writing a package for multivariate polynomials ('multipols')
> using S3 methods.
>
> The package includes a Ops.multipol()  function for the
> arithmetic methods;  I would like
> to define some sort of user-specified Boolean option which, if
> set,  would force results to be simplified as they are produced.
>
> Call this option "trim".  Trimming a multipol results in
> a smaller array that is more manageable.
>
> Mostly one wants to trim, sometimes not.
>
>
> Would options() be a good way to manage this?
>
> One issue is the behaviour of unary operators "+" and
"-".
>
> If trim is TRUE, then  "a"   is one thing,  but "+a" 
returns
> "trim(a)", which might be different.
>
> Also "1*a" would be different from "a" and
"a+0"
>
>
>
> Does the List consider this to be Good Practice?
>
> Has anyone got comments?
>
>
>
> --
> Robin Hankin
> Uncertainty Analyst and Neutral Theorist,
> National Oceanography Centre, Southampton
> European Way, Southampton SO14 3ZH, UK
>  tel  023-8059-7743
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>

> One issue is the behaviour of unary operators "+" and
"-".
>
> If trim is TRUE, then  "a"   is one thing,  but "+a" 
returns
> "trim(a)", which might be different.
>
> Also "1*a" would be different from "a" and
"a+0"
I think this is ok.  In the ggplot2 package I use + to join together
multiple plots, where a + b != b + a, and a + b + c (sometimes) = a.
This doesn't seem to cause much confusion for users.

Hadley

-- 
http://had.co.nz/