[R] library sets: A & EMPTY does not work; gset_intersection(A,EMPTY) works

[Czerminski, Ryszard]

It seems that "A & B" works the same way as "gset_intersection(A,B)"
as long as A and B are not empty...
see below:

fuzzy_logic("Yager", p=2)
support <- universe <- c('a','b','c','d')
A <- gset(support=support, memberships=c(0.2, 0.2, 0.9, 0),
universe=universe)
B <- gset(support=support, memberships=c(0.211, 0.222, 0.999, 0),
universe=universe)
A
B
A & B
gset_intersection(A,B)
E <- A - A
A & E
gset_intersection(A,E)

> fuzzy_logic("Yager", p=2)
> support <- universe <- c('a','b','c','d')
> A <- gset(support=support, memberships=c(0.2, 0.2, 0.9, 0),
universe=universe)
> B <- gset(support=support, memberships=c(0.211, 0.222, 0.999, 0),
universe=universe)
> A
{"a" [0.2], "b" [0.2], "c" [0.9]}
> B
{"a" [0.211], "b" [0.222], "c" [0.999]}
> A & B
{"c" [0.899995]}
> gset_intersection(A,B)
{"c" [0.899995]}
> E <- A - A
> A & E
Error in A & E :
  operations are possible only for numeric or logical types
In addition: Warning message:
Incompatible methods ("Ops.gset", "Ops.set") for "&"
> gset_intersection(A,E)
{}


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-----Original Message-----
From: Peter Ehlers [mailto:ehlers at ucalgary.ca] 
Sent: Wednesday, March 31, 2010 11:43 AM
To: Czerminski, Ryszard
Cc: R-help at r-project.org
Subject: Re: [R] library sets: A & EMPTY does not work;
gset_intersection(A,EMPTY) works

On 2010-03-31 9:30, Peter Ehlers wrote:
> Unless I'm missing something, I don't see any method
> in pkg:sets for intersection other than gset_intersection.

Whoops, a bit quick on the draw.
There are of course also set_intersection and cset_intersection,
but not AFAICS any method for `&`.

  -Peter Ehlers

> So you're using the base R function `&` whose help page
> tells you that its arguments should be vectors. Yours
> aren't.
>
> -Peter Ehlers
>
> On 2010-03-31 8:50, Czerminski, Ryszard wrote:
>> When using generalized sets from "sets" library
>>
>> A& EMPTY does not work, but gset_intersection(A,EMPTY) works: example
>> code below
>>
>> Is it a bug?
>>
>> Best regards,
>> Ryszard
>>
>> library(sets)
>> support<- universe<- c('a','b','c','d')
>> A<- gset(support=support, memberships=c(0.2, 0.2, 0.9, 0),
>> universe=universe)
>> class(A)
>> A
>> E<- A - A # create empty set
>> I<- gset_intersection(A, E) #<<< this WORKS
>> class(I); I
>> I<- A& E #<<< this DOES NOT WORK
>>
>> # ---
>>
>>> support<- universe<- c('a','b','c','d')
>>> A<- gset(support=support, memberships=c(0.2, 0.2, 0.9, 0),
>> universe=universe)
>>> class(A)
>> [1] "gset" "cset"
>>> A
>> {"a" [0.2], "b" [0.2], "c" [0.9]}
>>> E<- A - A
>>> I<- gset_intersection(A, E) #<<< this WORKS
>>> class(I); I
>> [1] "set" "gset" "cset"
>> {}
>>> I<- A& E #<<< this DOES NOT WORK
>> Error in A& E :
>> operations are possible only for numeric or logical types
>> In addition: Warning message:
>> Incompatible methods ("Ops.gset", "Ops.set") for "&"
>>
>>
>>
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-- 
Peter Ehlers
University of Calgary