[R] Create a vector of indices from a matrix of start and end points
George W. Gilchrist
gwgilc at wm.edu
Sat Sep 23 14:44:44 CEST 2006
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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