[R] Function for describing segements in sequential data

[Charles C. Berry]

On Wed, 27 Jan 2010, Gregory Gentlemen wrote:

> Dear R-users,
>
> Say that I have a sequence of zeroes and ones:
>
> x <- c(1,1,1,0,0,0,0,1,1,1,0,0,0,0,1,1,1,0,0,0,0)
>
> The sequences of ones represent segments and I want to report the 
> starting and endpoints of these segments. For example, in 'x', the first 
> segment starts at location 1 and ends at 3, and the second segment 
> starts at location 8 and ends at location 10. Is there an efficient way 
> of doing this in R without having to right a bunch of if-else 
> conditions? I know the rle function will report the length of the 
> segments but not the endpoints.

If this is more than a small one-off problem you might try this:

> require(IRanges) # from BioConductor
> IRanges(Rle(x)==1) # n.b. Rle != rle
IRanges of length 3
     start end width
[1]     1   3     3
[2]     8  10     3
[3]    15  17     3
>


HTH,

Chuck

>
> Thanks in advance.
>
> Gregory Gentlemen
>
>
>
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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