[R] Using indexing to manipulate data

[Gabor Grothendieck]

Here are two solutions.  The first uses merge and the second uses
sqldf.  They both do a self join picking off the unique pairs.  The
sqldf solution also sorts the result:

# input
DF <- structure(list(Actor = c("Jim", "Bob", "Bob", "Larry", "Alice",
"Tom", "Tom", "Tom", "Alice", "Nancy"), Act = c("A", "A", "C",
"D", "C", "F", "D", "A", "B", "B")), .Names = c("Actor", "Act"
), class = "data.frame", row.names = c(NA, -10L))

subset(unique(merge(DF, DF, by = 2)), Actor.x < Actor.y)

library(sqldf) # see http://sqldf.googlecode.com
sqldf("select A.Actor, A.Act, B.Act
	from DF A join DF B
	where A.Act = B.Act and A.Actor < B.Actor
	order by A.Act, A.Actor")



On Thu, Mar 18, 2010 at 1:05 AM, duncandonutz <dwadswor at unm.edu> wrote:
>
> I know one of R's advantages is it's ability to index, eliminating the need
> for control loops to select relevant data, so I thought this problem would
> be easy.  I can't crack it.  I have looked through past postings, but
> nothing seems to match this problem
>
> I have a data set with one column of actors and one column of acts.  I need
> a list that will give me a pair of actors in each row, provided they both
> participated in the act.
>
> Example:
>
> The Data looks like this:
> Jim         A
> Bob        A
> Bob        C
> Larry      D
> Alice      C
> Tom       F
> Tom       D
> Tom       A
> Alice      B
> Nancy    B
>
> I would like this:
> Jim      Bob
> Jim      Tom
> Bob     Alice
> Larry   Tom
> Alice    Nancy
>
> The order doesn't matter (Jim-Bob vs. Bob-Jim), but each pairing should be
> counted only once.
> Thanks!
>
> --
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>
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