R help - Sep 2006 - Create a vector of indices from a matrix of start and end points

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/

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/
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

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

What is the problem you are trying to solve?

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/
>
> ______________________________________________
> R-help@stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> 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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