hi all - quick question: i have a matrix m, say nrow=5, ncol=4. in a function i'd like to retrieve certain rows or columns from m, but which rows/cols are not known ahead of time. the function should return a sub-matrix (i.e. still of class 'matrix').
when selecting a single column (or row), the indexing operation converts the object of class 'matrix' into a vector of it's mode. e.g.: myfun <- function(m, cols) m[,cols]; m <- matrix(1:20, nrow=5); sm <- myfun(m, c(2)); the last line returns a vector, but i'd like to still get back a matrix (of dimensions 5,1). most of the time i'll be selecting groups of rows or cols, so this isn't a problem (as the return value remains a matrix), but on rare occasions a single selecting index will be passed, causing a problem for code further down that expects the 'sm' to be in matrix form (e.g. using the 'apply' function). is there any way to preserve the class of the matrix object when performing indexing? ______________________________________________ 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.
