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

From: David Barron <mothsailor_at_googlemail.com>
Date: Sat 23 Sep 2006 - 13:18:16 GMT

unlist(apply(tmp1,1,function(x) seq(x[1],x[2])))

On 23/09/06, George W. Gilchrist <gwgilc@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@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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> and provide commented, minimal, self-contained, reproducible code.
>

-- 
=================================
David Barron
Said Business School
University of Oxford
Park End Street
Oxford OX1 1HP

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Received on Sat Sep 23 23:22:33 2006

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