Dear Murali, Here is one way:
set.seed(123) a <- matrix(abs(rnorm(100)), 10) b <- rnorm(10) apply(a,2,function(x) ifelse(b>quantile(b,probs=0.75),-x,x)) HTH, Jorge On Wed, Nov 5, 2008 at 11:30 AM, <[EMAIL PROTECTED]> wrote: > Folks, > > I have a matrix: > > set.seed(123) > a <- matrix(rnorm(100), 10) > > And a vector: > > b <- rnorm(10) > > Now, I want to switch the signs of those rows of a corresponding to > indices in b whose values exceed the 75 %-ile of b > > which(b > quantile(b)[4]) > [1] 2 6 10 > > so I want, in effect: > > a[2, ] <- -a[2, ] > a[6, ] <- -a[6, ] > a[10, ] <- -a[10, ] > > I thought I could do > > a[which(b > quantile(b)[4]), ] <- -a > > but that's clearly wrong. > > I came up with an sapply(): > > t(sapply(1 : NROW(a), function(n) ifelse(b > quantile(b)[4], -a[n, ], a[n, > ]))) > > Ugh. > > What's a good way to achieve this? > > Thanks, > > Murali > > > --------------------------------------------------------------------------- > This e-mail is confidential and may be privileged. If you have received it > by mistake, please notify the sender by return e-mail and delete it from > your system. You should not disclose, copy or use it for any purpose. The > information in this e-mail is not contractual. Fortis Investments provides > no guarantee as to the correctness of this information and accepts no > responsibility for any action taken on the basis of it. Fortis Investments > is the trade name for all entities within the Fortis Investment Management > group. > > ______________________________________________ > 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. > [[alternative HTML version deleted]] ______________________________________________ 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.
