[BioC] IRanges: Trying to cut overlapping intervals into pieces

[Elizabeth Purdom]

Thanks for the help. It's much neater than what I had (and I do have 
gaps). If you are thinking about adding this kind of functionality, I'd 
be glad to tell you more specifically what I am doing if it helps to 
have a more general picture.

I kept thinking the intersect or setdiff would help for different 
things, but it wound up not doing what I needed. For example, it doesn't 
do pairwise, but across the entire set, right? I often had a set of 
intervals that I wanted to 'subtract' pairwise from another set of 
intervals. Just to know, is there a function that does that? I thought 
maybe 'narrow', but sometimes subtracting an interval would cut an 
existing interval into pieces, and narrow doesn't seem to do this.

Best,
Elizabeth

Michael Lawrence wrote:
> 
> 
> On Fri, Jan 23, 2009 at 10:24 PM, Elizabeth Purdom 
> <epurdom at stat.berkeley.edu <mailto:epurdom at stat.berkeley.edu>> wrote:
> 
>     Hi,
> 
>     I am trying to take overlapping intervals and return a set of
>     intervals that are not overlapping but cover all of the region (and
>     mantain the intervals that don't overlap). In particular, I don't
>     want to merge intervals that overlap together (i.e. the reduce
>     function in IRanges)-- I want to cut them up into distinct regions.
>     For example, if I have intervals:
>     [1,6], [4,8], [7,10]
>     I want to get back the set of adjacent intervals:
>     [1,3],[4,6],[7,8],[9,10]
> 
> 
> Well that's a fun one.
> 
> ir <- IRanges(c(1, 4, 7), c(6, 8, 10))
> adj <- IRanges(sort(unique(c(start(ir), head(end(ir),-1)+1))), 
> sort(unique(c(end(ir), tail(start(ir),-1)-1))))
> 
> ... is a not so nice one, but pretty fast..
>  
> But if you had a gap in those ranges, like:
> 
> ir <- IRanges(c(1, 4, 10), c(6, 8, 10))
> 
> So there's a gap at position 9, you would need an additional filtering step:
> 
> adj[adj %in% ir]
> 
> This last step requires the devel version of IRanges, but can be 
> emulated using !is.na <http://is.na>(overlap(ir, adj, multiple=FALSE)).
> 
> 
>     The options I find that look like they perhaps do this (intersect or
>     setdiff?) seem to be related to the 'normal' ranges class; but this
>     class requires a gap between intervals -- no adjacent intervals --
>     which is not what I want. Is there a nice way to do this with
>     IRanges (or a not so nice one, but fast)?
> 
> 
> The intersect and setdiff functions are for any Ranges, normal or not. 
> They return normal IRanges though. Perhaps the documentation does not 
> make this clear. They probably aren't very useful functions.
>  
> 
> 
>     Similarly, is there a 'reduce' version that doesn't merge adjacent
>     intervals but only truly overlapping ones? There are a lot of
>     annotation examples where you wouldn't not want to merge adjacent
>     intervals (e.g. UTRs)
> 
> 
> Try a trick like this:
> 
> ir2 <- IRanges(c(1, 5, 7), c(4, 6, 9))
> width(ir2) <- width(ir2) - 1
> rir2 <- reduce(ir2)
> width(rir2) <- width(rir2) + 1
> 
> Or find the overlap, reduce those that did overlap and combine that 
> result with those that did not overlap.
>  
> 
> 
>     Thanks for any assistance!
> 
> 
> Thanks for providing more use cases. We'll consider adding functionality 
> along these lines to the base package (actually the reduce one has been 
> on the TODO list for many months).
>  
> 
> 
>     Elizabeth Purdom
>     Division of Biostatistics
>     UC, Berkeley
> 
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