'[' is the 'subscript' or 'extraction', not 'subscription' operator: this is also called 'indexing', as in 'An Introduction to R'.
On Mon, 6 Nov 2006, Vladimir Dergachev wrote: > I was looking at the data frame subscription operator (attached in the end > of this e-mail) and got puzzled by the following line: > > class(x) <- attr(x, "row.names") <- NULL > > This appears to set the class and row.names attributes of the incoming data > frame to NULL. Actually no, it removes them: see ?attr and ?class. > So far I was not able to figure out why this is necessary - > could anyone help ? You need to remove the class to avoid recursion: a few lines later x[i] needs to be a call to the primitive and not the data frame method. > The reason I am looking at it is that changing attributes forces duplication > of the data frame and this is the largest cause of slowness of data.frames in > general. Do you have evidence of that? R has facilities to profile its code, and I have never seen [.data.frame taking a significant proportion of the total time. If it does for your application, consider if a data frame is an appropriate way to store your data. I am not sure we would accept that data frames do have 'slowness in general', but their generality does make them slower than alternatives where the generality is not needed. [...] -- 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 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
