[R] Finding overlaps in vector

[Charles C. Berry]

On Fri, 21 Dec 2007, Johannes Graumann wrote:

> <posted & mailed>
>
> Dear all,
>
> I'm trying to solve the problem, of how to find clusters of values in a
> vector that are closer than a given value. Illustrated this might look as
> follows:
>
> vector <- c(0,0.45,1,2,3,3.25,3.33,3.75,4.1,5,6,6.45,7,7.1,8)
>
> When using '0.5' as the proximity requirement, the following groups would
> result:
> 0,0.45
> 3,3.25,3.33,3.75,4.1
> 6,6.45
> 7,7.1

Try this:

> tmp <- rle( diff(v)<.5 )
> ends <- 1+cumsum(tmp$lengths)[tmp$values]
> mapply(function(x,y) v[ seq(to=x,length=y) ], ends, 1+tmp$lengths[tmp$values])
[[1]]
[1] 0.00 0.45

[[2]]
[1] 3.00 3.25 3.33 3.75 4.10

[[3]]
[1] 6.00 6.45

[[4]]
[1] 7.0 7.1


HTH,

Chuck

>
> Jim Holtman proposed a very elegant solution in
> http://tolstoy.newcastle.edu.au/R/e2/help/07/07/21286.html, which I have
> modified and perused since he wrote it to me. The beauty of this approach
> is that it will not only work for constant proximity requirements as above,
> but also for overlap-windows defined in terms of ppm around each value.
> Now I have an additional need and have found no way (short of iteratively
> step through all the groups returned) to figure out how to do that with
> Jim's approach: how to figure out that 6,6.45 and 7,7.1 are separate
> clusters?
>
> Thanks for any hints, Joh
>
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Charles C. Berry                            (858) 534-2098
                                             Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu	            UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901