Re: [R] Interaction versus combinations

From: Phil Spector <spector_at_stat.berkeley.edu>
Date: Thu, 03 Jun 2010 12:14:18 -0700 (PDT)

Perhaps not the best or easiest way, but does:

> apply(t(combn(idx,2)),1,paste,collapse='.')
[1] "1.3" "1.6" "1.9" "3.6" "3.9" "6.9"

get you in the right direction?

On Thu, 3 Jun 2010, Alex van der Spek wrote:

> I can get the interactions between factors like this:
>
>> idx=c(1,3,6,9)
>> jdx=idx
>> levels(interaction(idx,jdx,lex.order=TRUE))
> [1] "1.1" "1.3" "1.6" "1.9" "3.1" "3.3" "3.6" "3.9" "6.1" "6.3" "6.6" "6.9"
> [13] "9.1" "9.3" "9.6" "9.9"
>
> This list contains all possible interactions. Whereas I need only the
> combinations, e.g 4 over 2 = 6 total being
>
> "1.3 " "1.6" "1.9" "3.6" "3.9" "6.9"
>
> I have been unable to find how to get the combinations. Of course with some
> string manipulations this can be done for this toy example. There should be
> something in R to make this easy?
>
> Thanks in advance
> Alex van der Spek
>
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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. Received on Thu 03 Jun 2010 - 19:19:03 GMT

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