Hi [R-2.6.0, macOSX 10.4.10]. The helppage says that rowSums() and colSums() are equivalent to 'apply' with 'FUN = sum'. But I came across this: > a <- matrix(1:30,5,6) > is.integer(apply(a,1,sum)) [1] TRUE > is.integer(rowSums(a)) [1] FALSE > so rowSums() returns a float. Why is this? -- Robin Hankin Uncertainty Analyst National Oceanography Centre, Southampton European Way, Southampton SO14 3ZH, UK tel 023-8059-7743
On Fri, 9 Nov 2007, Robin Hankin wrote:> Hi > > [R-2.6.0, macOSX 10.4.10]. > > The helppage says that rowSums() and colSums() > are equivalent to 'apply' with 'FUN = sum'. > > But I came across this: > > > a <- matrix(1:30,5,6) > > is.integer(apply(a,1,sum)) > [1] TRUE > > is.integer(rowSums(a)) > [1] FALSE > >'equivalent' does not mean 'identical': the wording was deliberate.> so rowSums() returns a float.And that is what the help page says it does (albeit more accurately: there is no 'float' type, but there is numeric aka double and the result could be complex).> Why is this?You seem to be asking why R works as documented! -- Brian D. Ripley, ripley at stats.ox.ac.uk 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
On Tue, 20 Nov 2007, Tim Hesterberg wrote:> I wrote the original rowSums (in S-PLUS). > There, rowSums() does not coerce integer to double.Actaully, neither does R. It computes a double answer but does no coercion per se.> However, one advantage of coercion is to avoid integer overflow.Indeed, as I told Robin Hankin privately, that was the design reason.> > Tim Hesterberg > >> ... So, why does rowSums() coerce to double (behaviour >> that is undesirable for me)? > > ______________________________________________ > R-help at 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. >-- Brian D. Ripley, ripley at stats.ox.ac.uk 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