Hi, xr <- rev( x) vec <- 1:(length( x) - 1) rev( xr[ sequence( vec)] - rep.int( xr[ -1], vec))
On 2015-09-21 14:17:40, Dan D wrote: > I need an efficient way to build a new n x (n-1)/2 vector from an n-vector x > as: > > c(x[-1]-x[1], x[-(1:2)]-x[2], ... , x[-(1:(n-1)] - x[n-1]) > > x is increasing with x[1] = 0. > > The following works but is not the greatest: > junk<-outer(x, x, '-') > junk[junk>0] > > e.g., > given > x<-c(0, 3, 7, 20) > junk<-outer(x, x, '-') > junk[junk>0] # yields: c(3, 7, 20, 4, 17, 13) as needed, but it has to go > through > junk > # [,1] [,2] [,3] [,4] > #[1,] 0 -3 -7 -20 > #[2,] 3 0 -4 -17 > #[3,] 7 4 0 -13 > #[4,] 20 17 13 0 > > Anyone have a better idea? > > -Dan > > > > -- > View this message in context: > http://r.789695.n4.nabble.com/vector-manipulations-differences-tp4712575.html > Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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. > ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.
