R devel - Feb 2014 - suggestion for "sets" tools upgrade

First, let me apologize in advance if this is the wrong place to submit 
a suggestion for a change to functions in the base-R package.  It never 
really occurred to me that I'd have an idea worthy of such a change.

My idea is to provide an upgrade to all the "sets" tools (intersect, 
union, setdiff, setequal) that allows the user to apply them in a 
strictly algebraic style.

The current tools, as well documented, remove duplicate values in the 
input vectors.  This can be helpful in stats work, but is inconsistent 
with the mathematical concept of sets and set measure.  What I propose 
is that all these functions be given an additional argument with a 
default value:  "multiple=FALSE" .  When called this way, the
functions
remain as at present.  When called with "multiple=TRUE,"  they treat
the
input vectors as true 'sets' of elements.

I've already written and tested upgrades to all four functions, so if 
upgrading the base-R package is not appropriate, I'll post as a package 
to CRAN.  It just seems more sensible to add to the base.

Thanks in advance for any advice or comments.
(Please be sure to email, as I can't recall if I'm currently registered 
for r-devel)

Here's an example of the new code:

intersect<-function (x, y,multiple=FALSE)
{
     y <- as.vector(y)
	trueint <- y[match(as.vector(x), y, 0L)]
     if(!multiple) trueint <- unique(trueint)
	return(trueint)
}

thanks
Carl
-

On Thu, Feb 6, 2014 at 8:31 PM, Carl Witthoft <carl at witthoft.com>
wrote:
> First, let me apologize in advance if this is the wrong place to submit a
> suggestion for a change to functions in the base-R package.  It never
really
> occurred to me that I'd have an idea worthy of such a change.
>
> My idea is to provide an upgrade to all the "sets" tools
(intersect, union,
> setdiff, setequal) that allows the user to apply them in a strictly
> algebraic style.
>
> The current tools, as well documented, remove duplicate values in the input
> vectors.  This can be helpful in stats work, but is inconsistent with the
> mathematical concept of sets and set measure.
No comments about back-compatability concerns, etc. but why do you
think this is closer to the "mathematical concept of sets"? As I
learned them, sets have no repeats (or order) and other languages with
set primitives tend to agree:

python> {1,1,2,3} == {1,2,3}
True

I believe C++ calls what you're looking for a multiset (albeit with a
guarantee or orderedness).

Cheers,
Michael

On 14-02-06 8:31 PM, Carl Witthoft wrote:
> First, let me apologize in advance if this is the wrong place to submit
> a suggestion for a change to functions in the base-R package.  It never
> really occurred to me that I'd have an idea worthy of such a change.
>
> My idea is to provide an upgrade to all the "sets" tools
(intersect,
> union, setdiff, setequal) that allows the user to apply them in a
> strictly algebraic style.
>
> The current tools, as well documented, remove duplicate values in the
> input vectors.  This can be helpful in stats work, but is inconsistent
> with the mathematical concept of sets and set measure.
I understand what you are asking for, but I think this justification for 
it is just wrong.  Sets don't have duplicated elements:  an element is 
in a set, or it is not.  It can't be in the set more than once.



What I propose
> is that all these functions be given an additional argument with a
> default value:  "multiple=FALSE" .  When called this way, the
functions
> remain as at present.  When called with "multiple=TRUE,"  they
treat the
> input vectors as true 'sets' of elements.
>
> I've already written and tested upgrades to all four functions, so if
> upgrading the base-R package is not appropriate, I'll post as a package
> to CRAN.  It just seems more sensible to add to the base.
>
> Thanks in advance for any advice or comments.
> (Please be sure to email, as I can't recall if I'm currently
registered
> for r-devel)
>
> Here's an example of the new code:
>
> intersect<-function (x, y,multiple=FALSE)
> {
>       y <- as.vector(y)
> 	trueint <- y[match(as.vector(x), y, 0L)]
>       if(!multiple) trueint <- unique(trueint)
> 	return(trueint)
> }
This is not symmetric.  I'd like intersect(x,y,TRUE) to be the same as 
intersect(y,x,TRUE), up to re-ordering.  That's not true of your function:

 > x <- c(1,1,2,3)
 > y <- c(1,1,1,4)
 > intersect(x,y,multiple=TRUE)
[1] 1 1
 > intersect(y,x,multiple=TRUE)
[1] 1 1 1

I'd suggest that you clearly define what you mean by your functions, and 
put them in a package, along with examples where they give more useful 
results than the standard definitions.  I think the current base package 
functions match the mathematical definitions better.

Duncan Murdoch