[R] intersect() without discarding duplicates?

[David Winsemius]

On May 20, 2010, at 7:30 PM, Nordlund, Dan (DSHS/RDA) wrote:

>> -----Original Message-----
>> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
>> project.org] On Behalf Of Jonathan
>> Sent: Thursday, May 20, 2010 3:25 PM
>> To: David Winsemius
>> Cc: r-help
>> Subject: Re: [R] intersect() without discarding duplicates?
>>
>> Thanks, but that doesn't quite work, since I'd want the result of b[b
>> %in%
>> a] to be symmetric with a[a%in%b] (so if there are two 2's in EACH
>> vector,
>> I'll get two 2's in the result, but if there are two 2's in only one
>> vector,
>> but one two in the other, the result will show only one 2.
>>
>> Consider:
>>
>>> a <- c(2,4,3)
>>> b<-c(6,6,5,2,2,8,4)
>>
>>> b[b %in% a]
>> [1] 2 2 4
>>
>>> a[a%in%b]
>> [1] 2 4
>>
>> The second answer is correct, but I can't predict which variable to  
>> put
>> in
>> which position in the statement, so I'd need them both to be correct.
>>
>> Best,
>> Jonathan
>>
>
> I think you have misread the intersect documentation.  Given your  
> examples above intersect is what you in fact want.
>
>> a <- c(2,4,3)
>> b<-c(6,6,5,2,2,8,4)
>> intersect(a,b)
> [1] 2 4

He wants this result.

 > a <- c(2,4,2,3)
 > b<-c(6,6,5,2,2,8,4)
 > somefn(a,b)
[1] 2 4 2

And this result:

 > a <- c(2,4,3)
 > b<-c(6,6,5,2,2,8,4)
 > somefn(a,b)
[1] 2 4
 >somefn(b,a)
[1] 2 4


>
> Hope this is helpful,
>
> Dan
>
> Daniel J. Nordlund
> Washington State Department of Social and Health Services
> Planning, Performance, and Accountability
> Research and Data Analysis Division
> Olympia, WA 98504-5204
>
>
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David Winsemius, MD
West Hartford, CT