On Sat, 2007-09-15 at 09:02 -0700, Gerard Smits wrote: > Hi All, > > There are a variety of functions that can be applied to a variable > (column) in a data frame: mean, min, max, sd, range, IQR, etc.
But one their own, these are not equivalents to rowMeans, rowSums etc below. > > I am aware of only two that work on the rows, using q1-q3 as example > variables: > > rowMeans(cbind(q1,q2,q3),na.rm=T) #mean of multiple variables > rowSums (cbind(q1,q2,q3),na.rm=T) #sum of multiple variables If you really want to apply a function to the individual rows of a matrix-like object then apply() is your friend: ?rowMeans states: Details: These functions are equivalent to use of 'apply' with 'FUN = mean' or 'FUN = sum' with appropriate margins, but are a lot faster. So see ?apply and argument 'margin'. For rows use margin = 1, e.g.: dat <- matrix(runif(1000), ncol = 100) apply(dat, 1, mean) rowMeans(dat) > > Can the standard column functions (listed in the first sentence) be > applied to rows, with the use of correct indexes to reference the > columns of interest? Or, must these summary functions be programmed > separately to work on a row? You can only use those functions on a column via subsetting, e.g.: mean(dat[,4]) min(dat[,4]) If all you want is a single row (the equivalent of what you seem to be asking) then these also work: mean(dat[4,]) min(dat[4,]) HTH G > > Thanks, > > Gerard > > > > [[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. -- %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% Gavin Simpson [t] +44 (0)20 7679 0522 ECRC, UCL Geography, [f] +44 (0)20 7679 0565 Pearson Building, [e] gavin.simpsonATNOSPAMucl.ac.uk Gower Street, London [w] http://www.ucl.ac.uk/~ucfagls/ UK. WC1E 6BT. [w] http://www.freshwaters.org.uk %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% ______________________________________________ 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.