[R] subsetting a matrix with specified no of columns

[David Winsemius]

On Apr 8, 2010, at 7:39 AM, Lee William wrote:

> Hello! All,
>
> I am working on 10000x1000 matrix say 'mat' and i want to subset  
> this matrix
> in a fashion that in new matrix i get columns  
> 2,3,9,10,16,17,23,24.......so
> on. That is pair of columns after every interval of 7. I tried  
> following but
> i got an error which is obvious.

a <- mat[ , sort( c(seq(2, 1000, by=7), 1 +seq(2, 1000, by=7)))]

>
>> dim(mat)
> [1] 10000   10
>
>> a=mat[,c(seq(c(2,3),ncol(mat),7))]
> Warning messages:
> 1: In if (n < 0L) stop("wrong sign in 'by' argument") :
>  the condition has length > 1 and only the first element will be used
> 2: In if (n > .Machine$integer.max) stop("'by' argument is much too  
> small")
> :
>  the condition has length > 1 and only the first element will be used
> 3: In if (dd < 100 * .Machine$double.eps) return(from) :
>  the condition has length > 1 and only the first element will be used
> 4: In 0L:n : numerical expression has 2 elements: only the first used
>
> Is there any other way to do it?? Please, help!
>
> regards
> Lee
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org 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 Winsemius, MD
West Hartford, CT