On 18-09-2012, at 19:21, eliza botto wrote:
>
> Dear useRs,
> i had a matrix with 31 rows and 444 columns and i wanted to extract every
> 37th column of that matrix starting from 1. more precisely i wanted to select
> columns 1, 38,75, 112 and so on. then doing the same by starting from column
> number 2(2,39,76,113.......).
> i was advised to use
>> x[c(TRUE, rep(FALSE, 36)),]
> i works if it is start from first column but as i am very new to R i wanted
> to know what to do to make it work if i want to start column selection from
> column 2 and then from column 3 and so on.
> sorry for bothering you once again..
When you use my method you could do the following
f3 <- function(x,M,start=1) {
x[c(start,seq_len((length(x)-1)/M)*M+start)]
}
M <- 37
A <- 1:(3*M)
f3(A,M)
f3(A,M,start=1)
f3(A,M,start=2)
When start is too large you may get NA's in the result.
You may have to get rid of them.
Berend
______________________________________________
R-help@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.
