On Mon, 26 Jan 2004, Simon Cullen wrote: > On Mon, 26 Jan 2004 20:15:51 +0100, <[EMAIL PROTECTED]> wrote: > > > I want to conditionally operate on certain elements of a matrix, let me > > explain it with a simple vector example > > > > > >> z<- c(1, 2, 3) > >> zz <- c(0,0,0) > >> null <- (z > 2) & ( zz <- z) > >> zz > > [1] 1 2 3 > > > > why zz is not (0, 0, 3) ????? > <snip> > > > > in the other hand, it curious that null has reasonable values > > > >> null > > [1] FALSE FALSE TRUE > > What you have done there is create a boolean vector, null, of the same > length as z (and zz). > > For instance: > (z > 2) & (zz <- z) > =(F F T) & (T T T) (as assignment - presumably - returns T)
assignment returns the new value of zz, which as it is all non-zero coerces to the logical vector T T T > =(F F T). > > What will work is: > z <- c(1, 2, 3) > index <- z>2 > zz <- z * index Rather better I think is zz <- ifelse(z > 2, z, zz) or even ind <- z > 2 zz[ind] <- z[ind] -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
