[R] Create a vector of indices from a matrix of start and end points

[jim holtman]

try this:

> x <- rbind(c(2,5), c(7,9), c(15,20))
> x
     [,1] [,2]
[1,]    2    5
[2,]    7    9
[3,]   15   20
> unlist(mapply(seq, x[,1], x[,2]))
 [1]  2  3  4  5  7  8  9 15 16 17 18 19 20
>


On 9/23/06, George W. Gilchrist <gwgilc at wm.edu> wrote:
> I have a very large dataframe and wish to extract a subset of rows. I
> have a two column matrix listing the starting and ending indices of
> one subset on each row. My idea is to create a vector of indices that
> could be applied to the dataframe and I have a solution using a for
> loop (below). But surely there is some more elegant way to do this! I
> looked thorough the archives without success. Thanks for any ideas.
>
>  > tmp1 <- matrix(c(2,5,7,9,15,20), 3,2, byrow=T)
>  > tmp1
>      [,1] [,2]
> [1,]    2    5
> [2,]    7    9
> [3,]   15   20
>  > t.ind <- NULL
>  > for (i in 1:3) t.ind <- c(t.ind, seq(tmp1[i,1], tmp1[i,2]))
>  > t.ind
> [1]  2  3  4  5  7  8  9 15 16 17 18 19 20
>  >
>
> cheers, George
>
> ..................................................................
> George W. Gilchrist                           Email: gwgilc at wm.edu
> Director of Graduate Studies                 Phone: (757) 221-7751
> Department of Biology, Box 8795                Fax: (757) 221-6483
> College of William & Mary
> Williamsburg, VA 23187-8795
> http://gwgilc.people.wm.edu/
>
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>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?