R help - Jan 2009 - meaning of asymmetric on help page for intersect

Sorry if this is a silly question. What does asymmetric refer to from
?intersect, and are there any
aspects of the result that may be different from expected (reason for
exclamation point) ?

As toy data, if needed, here are the examples from the help page.

(x <- c(sort(sample(1:20, 9)),NA))
(y <- c(sort(sample(3:23, 7)),NA))

Thanks,

Juliet

There is also a symmetric set difference = union(setdiff(x, y),
setdiff(y, x))
denoted x \Delta y

-- David


-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Juliet Hannah
Sent: Tuesday, January 13, 2009 9:41 AM
To: r-help at r-project.org
Subject: [R] meaning of asymmetric on help page for intersect

Sorry if this is a silly question. What does asymmetric refer to from
?intersect, and are there any
aspects of the result that may be different from expected (reason for
exclamation point) ?

As toy data, if needed, here are the examples from the help page.

(x <- c(sort(sample(1:20, 9)),NA))
(y <- c(sort(sample(3:23, 7)),NA))

Thanks,

Juliet

______________________________________________
R-help at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

On 1/13/2009 10:41 AM, Juliet Hannah wrote:
> Sorry if this is a silly question. What does asymmetric refer to from
> ?intersect, and are there any
> aspects of the result that may be different from expected (reason for
> exclamation point) ?
There are two definitions for a set difference:  the symmetric one and 
the asymmetric one.

R uses the asymmetric one, so setdiff(A, B) is the intersection of A 
with the complement of B.  (The complement is taken in the union of A 
and B).

The symmetric difference is described on the Wikipedia page 
http://en.wikipedia.org/wiki/Symmetric_difference.  In R, you could get 
it as

union(setdiff(A, B), setdiff(B, A))

Duncan Murdoch
> 
> As toy data, if needed, here are the examples from the help page.
> 
> (x <- c(sort(sample(1:20, 9)),NA))
> (y <- c(sort(sample(3:23, 7)),NA))
> 
> Thanks,
> 
> Juliet
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

Hello,

The symmetric set difference of A and B is the set of elements in A or B
but not in A intersection B, i.e., ( (A U B) \ (A intersection B) ).

The asymmetric set difference of A and B is the set of elements of A
except those in B, i.e., (A \ B).

Best regards,

Carlos J. Gil Bellosta
http://www.datanalytics.com

Because there is also a symmetric difference: see

http://en.wikipedia.org/wiki/Symmetric_difference
> Sorry if this is a silly question. What does asymmetric refer to from
> ?intersect, and are there any
> aspects of the result that may be different from expected (reason for
> exclamation point) ?
>
> As toy data, if needed, here are the examples from the help page.
>
> (x <- c(sort(sample(1:20, 9)),NA))
> (y <- c(sort(sample(3:23, 7)),NA))
>
> Thanks,
>
> Juliet
-- 
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 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

... which is the same as

setdiff(union(x, y), intersect(x, y))

-Christos 
> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of 
> davidr at rhotrading.com
> Sent: Tuesday, January 13, 2009 10:56 AM
> To: Juliet Hannah; r-help at r-project.org
> Subject: Re: [R] meaning of asymmetric on help page for intersect
> 
> There is also a symmetric set difference = union(setdiff(x, 
> y), setdiff(y, x)) denoted x \Delta y
> 
> -- David
> 
> 
> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org]
> On Behalf Of Juliet Hannah
> Sent: Tuesday, January 13, 2009 9:41 AM
> To: r-help at r-project.org
> Subject: [R] meaning of asymmetric on help page for intersect
> 
> Sorry if this is a silly question. What does asymmetric refer 
> to from ?intersect, and are there any aspects of the result 
> that may be different from expected (reason for exclamation point) ?
> 
> As toy data, if needed, here are the examples from the help page.
> 
> (x <- c(sort(sample(1:20, 9)),NA))
> (y <- c(sort(sample(3:23, 7)),NA))
> 
> Thanks,
> 
> Juliet
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> 
>